How to check the ABS sensor with a tester or multimeter, find out its performance using an oscilloscope, test diagram + video and other nuances of the issue

The task of the anti-lock braking system (ABS), installed on the vast majority of modern cars, is to prevent the car from skidding during heavy braking. To do this, a special device is built into each hub, transmitting information about wheel rotation to the electronic control unit. Since a malfunction of this element is often the cause of system failure, the car owner should know how to check the ABS sensor in a garage.

Methods for checking the ABS sensor

ABS sensors play an important role in the operation of the car's braking system - the braking efficiency and uninterrupted operation of the unit as a whole depend on them. The sensor elements send data about the degree of rotation of the wheels to the control unit, and it analyzes the incoming information, building the desired algorithm of actions. But what to do if you have doubts about the serviceability of the devices?

Replacing the ABS block

For repair you need to prepare:

key "13";
ratchet;
head "10".

The procedure for working with Priora is as follows:

Stop the car and raise it. Disconnect the minus from the battery.
Drain the brake fluid from the cylinder brake hose.
Unscrew the brake pipes connected to the block. There are 6 of them in total.
Unhook the power lock and disconnect the wires.
Unscrew the nuts fastening to the car body.
Slowly pull the block and remove it.
Install the unit by connecting everything in reverse order. Don't forget to bleed the brake system.

Symptoms of a device malfunction

The fact that the ABS sensor is faulty will be indicated by an indicator on the instrument panel - it lights up when the system is deactivated, which turns off even if there is the slightest problem.

Evidence that ABS has ceased to “interfere” with the operation of the brakes:

Wheels constantly lock during heavy braking.
There is no characteristic knocking noise with simultaneous vibration when pressing the brake pedal.
The speedometer needle is delayed relative to acceleration or does not move from its original position at all.
If two (or more) sensors on the dashboard are faulty, the parking brake indicator also lights up and does not go out.

The ABS indicator on the dashboard indicates a system malfunction

What to do if the ABS warning lamp on the car’s dashboard does not behave quite correctly? You should not immediately change the sensor; first, the devices should be checked - this procedure can be performed independently, without resorting to the services of highly paid craftsmen.

Ways to check functionality

To determine the condition of a part, we will perform a series of steps to diagnose it, moving from simple to complex:

Let's check the fuses by opening the unit (inside the passenger compartment or in the engine compartment) and inspecting the corresponding elements (indicated in the repair/operation instructions). If a burnt component is found, we will replace it with a new one.
Let's inspect and check:
wiring for abrasions that increase the risk of a short circuit;
contamination of the part, possible external mechanical damage;
fixation and connection to ground of the sensor itself.

If the listed measures do not help to identify a device malfunction, it will have to be checked using instruments - a tester (multimeter) or an oscilloscope.

Tester (multimeter)

This method of diagnosing the sensor will require a tester (multimeter), instructions for operating and repairing the car, as well as PIN - wiring with special connectors.

The device combines the functions of an ohmmeter, ammeter and voltmeter

Tester (multimeter) is a device for measuring electric current parameters, combining the functions of a voltmeter, ammeter and ohmmeter. There are analog and digital device models.

To obtain complete information about the performance of the ABS sensor, you need to measure the resistance in the device circuit:

We lift the car with a jack or hang it on a lift.
Remove the wheel if it prevents access to the device.
Remove the cover of the system control unit and disconnect the controller connectors.
We connect the PIN to the multimeter and the contact socket of the sensor (the connectors for the rear wheel sensors are located inside the cabin, under the seats).

We connect the PIN to the tester and the contact socket of the sensor

The device readings must correspond to the data specified in the repair and operation manual for a particular vehicle. If the device resistance:

below the minimum threshold - the sensor is faulty;
approaches zero - short circuit;
unstable (jumping) at the moment of twitching of the wire - a violation of contact inside the wiring;
infinity or no readings - wire break.

Attention! The resistance of the ABS sensors on the front and rear axles is different. The operating parameters of the devices are 1–1.3 kOhm in the first case and 1.8–2.3 kOhm in the second.

Video “Diagnostics of the ABS sensor”

How to check using an oscilloscope (with connection diagram)

In addition to self-diagnosis of the sensor with a tester (multimeter), it can be checked using a more complex device - an oscilloscope.

The device examines the amplitude and time parameters of the sensor signal

An oscilloscope is a device that studies the amplitude and time parameters of a signal, which is intended for accurate diagnosis of pulse processes in electronic circuits. This device detects problems with connectors, broken connections to ground, and broken conductors. The test is performed by visually observing the vibrations on the device display.

To diagnose the ABS sensor with an oscilloscope, you must:

Fully charge the battery so that during the measurement you can observe voltage drops (jumps) on the connectors or conductors.
Find the touch sensor and disconnect the upper connector of the part.
Connect an oscilloscope to the contact socket.

Connecting the device to the ABS sensor connector (1 - toothed disc-rotor; 2 - sensor)

The serviceability of the ABS sensor is indicated by:

equal amplitude of signal fluctuations when the wheels of one axle rotate;
absence of amplitude beats when diagnosing with a sinusoid signal of lower frequency;
maintaining a stable, even amplitude of signal fluctuations not exceeding 0.5 V when the wheel rotates at a frequency of 2 rps.

Note that an oscilloscope is a rather complex and expensive device. Modern computer technologies make it possible to replace this device with a special program downloaded from the Internet and installed on a regular laptop.

Video “Laptop instead of an oscilloscope”

Checking a part without instruments

The easiest way to diagnose a device without instruments is to check the magnetic valve on the induction sensor. Any metal product (screwdriver, wrench) is applied to the part inside which the magnet is installed. If the sensor does not attract it, it is faulty.

Most anti-lock brake systems of modern cars have a self-diagnosis function with errors displayed (in alphanumeric encoding) on the on-board computer screen. You can decipher these symbols using the Internet or the machine’s operating instructions.

How to fix problems

After checking with instruments and identifying the faulty unit, you can begin repairs. Some owners repair the sensors by replacing the wiring harness or rewinding the coil.

Sensor failure

A faulty passive type sensor can be repaired yourself:

Remove the sensor from the hub. The fastening bolt often becomes sour, so you should unscrew it carefully. For removal it is allowed to use WD40 type fluid.
Remove the protective coil housing. Removal is done with a file. The cut should be done extremely carefully so as not to damage the housing and winding.
Remove the protective film from the winding by prying it off with a sharp knife.
Carefully unwind the wire from the spool. During the removal process, the version of a conductor break is confirmed. As a result, you will be left with an empty ferrite core, resembling a spool of thread in shape.
Wind a new winding. Copper wire from the coils of common relays of the RES-8 type can be used as a conductor. Winding can be done using a drill with smooth speed control. Be careful as breaking the wire will return you to the start. It is recommended to wind the conductor to the top level of the coil.
Check resistance. Most coils have a value in the range of 0.9-1.2 kOhm. To clarify, it is recommended to measure the parameter on a known-good sensor located on the opposite side of the axis. The resistance is adjusted by unwinding the excess wire. If the reading is low, you will need to use another wire or re-wind. Secure the wire from unraveling with tape or other adhesive tape.
Solder the wires to the coil terminals that serve as a connection between the winding and the harness. For outputs, it is recommended to use multi-core insulated cable, which has increased strength.
Install the coil into the old housing. If it received significant damage when disassembling the device, then the coil is filled with epoxy resin. To do this, the part is located in a metal container of a suitable size, for example, a capacitor housing. The air gap between the coil and the glass is carefully filled with resin. When pouring, it is advisable to avoid large air voids. After the resin has completely hardened, the body is removed.
Reinstall the sensor mount, securing it with epoxy resin. Conduct a visual inspection of the product for cracks and voids in the insulation. Detected defects are filled with resin.
Place the repaired sensor in its original place and check the functionality of the ABS system. When installing the device, it may be necessary to modify the resulting body, which is done with a file and sandpaper. The field installed sensor should have a gap between the coil and the toothed ring within 0.9-1.1 mm. When reducing the gap, it is recommended to bring it up to standard by installing gaskets.

It is necessary to drive the car for some time, checking the operation of the brakes at different speeds. There are cases when the ABS spontaneously activates at certain wheel speeds - usually just before stopping. Then you will need to search for the gap, adjusting it with shims or sharpening the sensor body.

Another repair option is to install a modified crankshaft position sensor from domestic cars:

Remove the “original” sensor and modify the body of the “donor” part. Most often, this role is played by the DPKV from the ZMZ-406 engine, which has a resistance within 800 Ohms. When modifying, you should strive to ensure a parallel arrangement of the core with the wound coil and the toothed ring mounted on the axis. The gap between the sensor and the ring should be within 0.2-0.3 mm.
Test the operation of the device. On some Japanese-made cars, the ABS lamp may turn on periodically. The situation is corrected by changing the connection of the harness contacts.

Both options for repairing the sensor require perseverance and the ability to work with various tools from the owner. If the car user doubts his abilities, it is recommended to purchase a new device or find the product at a car dismantling site.

Wiring problem

If the problem of sensor loss of functionality lies in the wiring, then it can be replaced:

Unscrew the sensor mount to the wheel hub.
Disconnect the wire plug.
Remove the sensor along with the wire. This will require removing the mounting brackets installed on the wiring.
Measure the installation distances of the brackets. It is recommended to draw a diagram and photograph the factory location of the fasteners.
Cut the sensor from the wire, leaving some extra length for soldering.
Check the integrity of the remaining cable on the sensor. If the section is intact, then you can begin installing a new wiring segment.
Remove all protective covers and fastenings from the old cable.
Select a wire with a suitable outer diameter and cross-section.
Install the previously removed protection and fastening elements onto the new harness. To facilitate assembly, it is recommended to use a soap solution.
Solder the sensor and plug into place.
Carefully isolate the joint. The accuracy of operation and service life of the repaired part depend on the tightness of the connection.
Reinstall the sensor, check the functionality of the ABS system, and make sure there are no errors during operation.

What to do if a breakdown is detected

What to do with the ABS sensor if a malfunction is detected? If the problem point is the device itself, it will have to be replaced, but in the case of electrical wiring, you can fix the defect yourself. To restore its integrity, we use the “soldering” method, carefully wrapping the joints with insulating tape.

If the ABS indicator on the dashboard lights up, this is a clear sign of a sensor failure. The described steps will help identify the cause of the breakdown, but if you lack knowledge and experience, it is better to contact a car service center. Otherwise, illiterate diagnostics of the condition, coupled with improper repair of the device, will reduce the effectiveness of the anti-lock braking system and can provoke an accident.

Checking the ABS sensor yourself. How to check the ABS sensor in different ways?

Even children probably know what ABS ( Anti-lock Braking System This system allows you to perform the most effective braking to stop the vehicle as quickly as possible. The system is electronic and is equipped with many sensors and a control unit, which ensures that the wheels do not lock during braking, that is, “do not skid.” Such an invention saves hundreds or maybe even thousands of lives on the road every day. The ABS system prevents skidding and loss of control, which is very important on slippery roads, as well as in case of emergency braking.

In this article, I will tell you how to check the ABS sensor if it malfunctions, as well as if an emergency indicator appears on the dashboard in the form of three English letters “ABS”. You will learn how to test the ABS sensor at home in various ways using a multimeter.

The most common breakdown in the ABS system is a circuit break, when communication is lost between the control unit and the sensor. This can happen for various reasons, which you will learn about a little later.

Let's sum it up

There are many breakdowns that can affect the ABS system. But the most common type of malfunction is sensor failure. If your car's anti-lock braking system is showing problems, the first thing you should do is check the sensors. There are several methods for testing the correct operation of these parts, so you can choose the most convenient testing option. However, diagnostics alone will not help the matter; any problems that have arisen will have to be corrected.

Today you can find and purchase ABS sensors from any manufacturer. You can find both simple parts for replacing factory sensors and original system elements at very affordable prices. And selection in this case will play a very important role. Use the factory catalogs to select sensors that are completely suitable for your vehicle and match the functions of the ABS system. To ensure that the anti-lock braking system does not interfere with the quality operation of the car, but helps to perform important tasks when braking, monitor the serviceability of the sensors and carry out diagnostic and repair work in a timely manner. Moreover, you can change the sensors of this system yourself. How often does ABS show problems in your car?

How to recognize a faulty ABS system or ABS sensor?

As I already said, the corresponding indicator lights up on the panel; this can happen while driving, braking, or when turning the key in the ignition. In the latter case, the appearance of the inscription indicates self-diagnosis of the system; after you start the engine, the light should go out.

If the ABS system malfunctions during braking, you will not hear the characteristic sound of the ABS unit located under the hood and will not feel the vibration that occurs when you sharply press the brake pedal and try to slip the wheels.

What to do first?

It is necessary to check the ABS sensors located near each wheel hub. Your task is to detect a violation in the connection of the sensors, a broken wire or damage to the ABS sensor housing. In any of these cases, you will one way or another see the corresponding indicator on the panel, well, provided that the system control unit itself is working and not “buggy”.

Checking the ABS sensor - measuring the resistance

We jack up the wheel on which you think the inoperative or faulty sensor is located, or each wheel in turn if you don’t know exactly which sensor is faulty.
Next, remove the wheel and gain access to the sensor.
Remove the housing, as well as the protective control unit and connectors that supply power to the sensors.
After that, we insert wires into the circuit of wires with PIN connectors and connect them with the sensor and multimeter.
We measure the resistance and compare it with the one that should be by default (you can find it in the manual) or with a representative of the manufacturer of your car.
We check the wiring for breaks or short circuits.
Rotate the wheel while watching the multimeter readings, the resistance should change.

Device - leg - 5-26 Ohm.
Device - "ground" - from 20 kOhm or more.

For more details on how to check the ABS sensor, watch this video:

Checking the ABS sensor using a tester - measuring the voltage

Let's jack up the wheel.
Turn on the multimeter, set the DC voltage measurement mode.
We connect the electrodes of the device to the connectors and check the readings, while rotating the wheel (about 1 rpm).
A working ABS sensor will show voltage on the device

0.25-1.2 Volts. If the wheel rotation speed is higher, the readings will increase accordingly.

How to check a sensor with an oscilloscope?

To diagnose the serviceability or malfunction of the ABS sensor, you can even use an oscilloscope or, more simply, a tester. When connected, a graph will be displayed on the device; using amplitude analysis, you can judge the serviceability or malfunction of the sensor.

The problem is that this device is not available at every service station, not to mention the garage in which you are going to conduct all your “experiments”. The device is expensive and quite difficult to understand, so to work with it you need to have certain knowledge and skills.

In modern cars, the ABS system has a self-diagnosis function; using special software, you can read the error code and then decipher it using a special table.

What indicates a faulty ABS

Reading ABS errors using a conventional car scanner usually does not give the result that the driver expects. Car service centers have the necessary diagnostic equipment and tools. But if you don’t want to immediately contact the service, analyze the situation. An ABS malfunction is indicated by:

ABS light comes on;
Poor brake pedal response;
The need to apply great force to the brake pedal;
Brake jamming.

Get out on a smooth road and check how the brakes work. If they behave randomly, engage at the wrong time, or the braking force does not match the pedal force, one of the ABS system components may be damaged. In many cases, these problems also indicate a malfunction of the calipers, brake cylinders, or depressurization of the brake line . However, if the ABS warning light constantly lights up, the driver should check the sensors of this system.

Is it possible to repair the ABS sensor?

The question of whether it is possible to repair this sensor is difficult to answer unequivocally; it increasingly depends on the degree of its damage and malfunction. If it’s all about simple damage to the wiring, then solving the problem will not be difficult. If the damage is more global, the core or winding is damaged, then most likely repairing such a sensor will simply not be possible and will require a complete replacement. Despite the fact that 99% of experts recommend replacing the sensor if it malfunctions or has problems with the winding, there are those who successfully restore these sensors at home using improvised means. You can find out more about this repair in the video below.

This video clearly demonstrates how to repair an ABS sensor at home.

That's all for me. Thank you for your attention, I hope you found it interesting and were able to learn something new for yourself. I look forward to your comments on this topic, perhaps you have encountered such a problem or managed to solve it. Until next time, bye.

How to check the ABS sensor for functionality?

Method of operation of the anti-lock brake system

A strong press on the brakes is detected by sensors, and the system deciphers this as the car skidding. There is a signal about the need to reduce the braking force. The pressure of the special fluid in the brake line decreases, and the wheels are unlocked. Didn't succeed the first time? The system will continue to try until the brake pad tension is relieved. The operation of ABS is schematically: braking - analysis - disinhibition process.

The system's response speed is very high. It starts working even before the wheel locks. The driver sees a corresponding signal on the control panel and feels characteristic shocks in the pedal. If the warning message does not disappear from the screen, this indicates a problem.

You should not rely entirely on the system. It creates a false illusion of driving safety for the driver. It is not always possible to shorten the braking distance of ABS, especially when it comes to cornering. In addition, the system is difficult to predict. A motorist is rarely able to determine where his braking distance ends.

Should I be afraid of ABS malfunctions? This system does not need repair often, as it is equipped with fuses and special relays. Failure means that the brakes now work without additional control, but this does not directly affect their functionality. So you can drive a car with a problematic anti-lock braking system, but it’s better not to. Many drivers ignore the danger and overestimate their level of control over the vehicle. Even the most experienced motorist can make mistakes when braking in an emergency. So as soon as the first signs of a malfunction appear, repair it.

Briefly about the principle of operation

The ABS function simulates the harsh, repeated pressure on the brake pedal experienced by drivers of older cars on slippery roads. Electronics uses this method of braking much more efficiently, locking and “releasing” the wheels several times per second. The operating algorithm is as follows:

During sudden braking, the control unit monitors the behavior of the wheels using sensors.
If one or more wheels stop rotating, the ECU issues a command to a hydraulic valve that releases fluid from that circuit. The pads stop holding the disc and rotation resumes.
By comparing the readings of all meters, the controller makes sure that braking is not complete and closes the hydraulic valve, and the wheel is blocked again. The cycle, lasting a fraction of a second, is repeated until the machine stops completely.

Important! If the functionality of one or more sensors is impaired, the ABS will fail entirely, since the electronic unit will not be able to compare the behavior of the wheels.

The latest generation ABS sensor is a coil with a semiconductor element installed in a stationary part of the hub. In the immediate vicinity of it, a toothed ring is attached to the brake disc, whose rotation is monitored by a sensor. It happens like this: the controller supplies voltage to the device, and it constantly changes the resistance due to the passage of a series of teeth on a rotating ring.

When the amount of electrical resistance becomes constant, the ECU regards this fact as wheel locking and turns on the above-described algorithm. If the element fails, the ABS system is completely disabled.

Signs of sensor malfunction

The following symptoms indicate that the ABS sensor needs to be checked:

when braking sharply or on a slippery road, the car moves “skid” and goes into a skid;
there is no characteristic sound of ABS activation - frequent tapping or crackling from the side of a locked wheel (the type of noise depends on the make of the car);
The anti-lock braking system warning light on the dashboard lights up.

If, for various reasons, the functionality of several sensors is disrupted, then the indicator for turning on the handbrake or a malfunction of the brake system additionally flashes on the instrument panel. You can continue to operate the car, but in slippery areas or during an emergency stop, the driver will have to work instead of ABS - often and sharply press the pedal.

Causes and symptoms of ABS problems

The sensor wire broke and the controller unit broke. Signals about angular velocities are not transmitted, the error signal lights up, and the system turns off.
Wheel sensors are faulty. The system turned on, performed self-diagnosis, found an error, and continued working. The contacts have oxidized, the connection to the system power supply is broken. Another possibility is that the wheel sensors have shorted to ground.
Tires have different pressures, different tread patterns, and different degrees of rubber wear. One of the wheels goes slower than the others. Indications of angular velocity are transmitted by an additional device.
Mechanical damage to parts: separators and grilles may break, the hub bearing may wear out, play may appear, the wheel sensor rotor may break, and the operation of the pump may be disrupted. Mechanical causes of the malfunction prevent the ABS from even starting.

Most of the above problems can be solved on your own. After all, complete replacement of equipment is very expensive. As the experience of auto mechanics shows, wheel sensors break more often than other parts. They are located next to the hubs and take on all the dirt. By examining them, you can begin the diagnosis.

The most unpleasant thing that can happen is that the control unit turns out to be faulty. And it is very expensive. But the complex works with a protective relay and rarely creates problems for the motorist. Therefore, you can check the block last. The procedure begins with the front wheels:

remove the sensor, clean with kerosene, white spirit;
checking the ABS sensor involves a thorough inspection of the wheel hub teeth. The revolutions are read from them. Dirty, clogged teeth - incorrect information and system freeze;
remove and clean the reverse gear sensor;
how to check if the electrical resistance is correct? Compare with the readings from the car's factory manual:
lift the body with a jack, spin the wheel, and while rotating, measure what voltage passes through the sensor winding. Compare with indicators from the directory;
check the bearings. A worn hub is one of the most common causes of problems. After cleaning with kerosene and checking by shaking, the faults will become obvious. Replace parts if necessary. Use a multimeter to check the operation of the sensor.

Did the procedure fail? The next step is checking the protective relay. Its location is indicated on the car wiring diagram. The device has aluminum walls and a plastic cover. There are a couple of fuses inside and it is quite possible that one of them simply burned out. When buying a car on the secondary market, you need to inquire about the location of the protective relay from the previous owner.

Are the fuses ok but the system is still faulty? Let's diagnose the relay itself:

disconnect the electrical connector;
connect the voltmeter probes to the first two numbered block pins;
turn on the ignition, measure the network voltage - 20V. There is no voltage - check the negative connector to see if the connection has gone to ground of the car;
remove the relay, connect to the battery (terminals number 5 and 6). Give 12 V. Clicks are heard - the device is working, if not - it needs to be replaced.

How is the check performed?

Since the operation of a working ABS sensor is based on changes in electrical resistance when the wheel rotates, its parameters can be measured with a multimeter or a tester operating in ohmmeter mode. Conditions for diagnostics: a regular garage or a flat area, an inspection ditch is not required. From the tools, take a jack and a wheel wrench.

To check the ABS sensor with a tester, follow these steps:

Place the car on a level surface and secure it with wheel chocks. The handbrake should not be applied.
Jack up the rear wheel and remove it. Having found the wiring harness going to the sensor in the hub, find the connector and disconnect it. Clean all contacts thoroughly, preferably with a special liquid.
Turn on the multimeter to measure resistance and take measurements in the block coming from the sensor. Depending on the brand of car, the value should be from 500 Ohm to 1.4 kOhm.
Grab the drum or disc with your hand and spin it while watching the tester readings. The resistance must change.
Switch the device to voltage measurement mode and turn on the ignition. Check the presence of DC current from the control unit by connecting a multimeter to the second part of the connector.
Repeat the operation on all wheels.

On different car models, the connector may be located in different places - hidden under the bottom or plastic protection. To locate the block, probe the wiring harness by hand.

Varieties of design

To calculate the angular speed of wheel rotation, 2 types of ABS sensor devices can be used:

based on an inductive element. They are also called passive, since the sensitive element does not require external power, and the operating principle itself is based on the effect of electromagnetic induction. Despite the simplicity of design and reliability, such devices are becoming less and less common on modern cars. The main drawback of the design is that at low vehicle speeds it is impossible to adequately calculate the wheel speed;
sensors based on the Hall effect. They are also called active, since the sensitive element needs power - a reference voltage. The signal produced by such speed sensors allows the ECU to more accurately calculate the wheel speed.

Design, principle of operation of inductive ABS sensors

Due to the operating principle of electromagnetic induction, the passage of comb teeth mounted on the CV joint body near the iron core provokes voltage surges. Due to the rotation of the wheel, a sinusoidal voltage fluctuation is recorded at the terminals of the ABS sensor; the frequency of the alternating voltage is directly proportional to the angular speed of rotation of the wheel.

The anti-lock brake system control unit registers and compares analog signals from all sensitive elements, which makes it possible to calculate the difference in the angular speeds of rotation of the wheels.

Multimeter test method

If you know how to use a multimeter, then you can check the passive ABS sensor using even the cheapest universal meter. Correspondence of possible faults and methods for their diagnosis:

open circuit of the coil winding. Set the multimeter to diode testing mode. If the device shows infinite resistance, then there is an open circuit in the circuit;
unsoldering the coil winding contacts. The nature of the failure is the same as in the case of a break;
short circuit. To check, switch the multimeter to resistance measurement mode - ohmmeter, measurement range - up to 20 kOhm. Pre-measure the resistance of a previously working sensor or find out the standard value from the technical documentation. Typically, the resistance of serviceable elements ranges from 0.7 to 2.5 kOhm. It is important to take into account that the resistance of working sensors on the front and rear axles can differ significantly.

If the ABS sensor is removed from the car, then you can simulate the rotation of the master disk with any magnetic metal object.

Due to the aggressiveness of the installation environment, ABS sensors on motorcycles may have an electromagnet instead of a permanent magnet, which must be taken into account when checking without dismantling (the ignition must be on).

How to make your search easier

In order not to carry out testing with a tester on each wheel separately, remove the connector of the ABS control unit. The video shows that once you understand the pinout, you can quickly find which circuit has a short circuit or an open circuit.

Application of the Hall effect

The operating principle of the Hall sensor is based on the effect of a transverse potential difference when a conductor with direct current is placed in a magnetic field. A change in the magnetic field when a gear passes near the sensing element provokes the occurrence of rectangular voltage surges. The pulse frequency allows the ABS control unit to calculate the actual wheel speed.

Diagnostic method

Since the operating principle of the ABS sensor is based on the Hall effect, its independent testing is similar to diagnosing the speed sensor used in the speedometer, DPKV. A full check of the correctness of the signal can only be carried out with an oscilloscope, but for simple diagnostics a regular multimeter will do.

To check, you need to switch the tester to DC voltage measurement mode. Connect the test leads to the signal contacts of the sensor, having previously supplied power through an additional resistance (a resistor with a value of 480 Ohms to 1.2 kOhms) and connecting the ground contact to an unpainted part of the car body. If the element is completely faulty, the marker disc rotating with the CV joint will not provoke a change in high and low voltage levels.

Offline check

To operate, the sensitive element requires reference power, so without an external EMF source capable of delivering 9-12 V, it will not be possible to check the ABS sensor with a multimeter. It will also be necessary to include an additional resistor in the circuit (in the case of the Opel Vectra C brake system, as shown in the video, an element with a rating of 680 Ohms will be sufficient). The pinout of the connector can be found in the repair and operating manual for your car.

Since the sensitive element will be removed from the car, you can simulate the rotation of the marker disk by moving the magnet near the sensitive element.

General recommendations for diagnosing the ABS system

If the circuit is broken, the self-diagnosis of the ABS system will necessarily record the fact of a decrease in resistance in the sensor circuit and light up the ABS fault light on the dashboard. Some systems are capable of not only recording the fact of an error, but also calculating which wheel the breakdown occurred on. Therefore, if possible, the first step is to conduct computer diagnostics. On many cars, if more than 1 sensor breaks down, the system lights up not only the ABS fault light, but also the parking brake indicator, after which the ABS turns off.

Before starting diagnostics with a multimeter, make sure that the air gap between the sensor and the marker disk is set correctly, and that the cavities of the marker disk themselves do not have dense dirt or corrosive deposits.

Be extremely careful when removing the sensor. They often stick, but impacts or other use of brute force can damage the plastic case. When installing, ensure that there is a correct air gap between the drive disc and the sensing element.

Analysis of diagnostic results

The problem with the ABS function does not always lie in the sensors. The culprits of system failure may also be the wires connecting the elements to the control unit. That is why it is necessary to carry out 3 measurements and draw the following conclusions based on the results:

If the resistance of the ABS sensor tends to zero or, conversely, the device shows an infinity symbol, then there is a malfunction of the element itself. Another option is a violation of the insulation or a break in the section of conductors from the connector to the sensor.
The tester shows that the resistance is within normal limits, but when the brake disc rotates, its value remains constant. There are two versions here: severe contamination of the gear ring (as an option - destruction) and, again, failure of the sensor.
The absence of voltage in the supply line indicates a break in the electrical circuit coming from the controller.

In the first case, it is necessary to remove the device from the hub and inspect the wires for fractures, breaks or short circuits. To be sure, measure the resistance again, while moving the conductors. If the result is negative, buy and install a new part.

If the resistance remains the same, get to the gear ring, clean it thoroughly and inspect it. If you find mechanical damage, it is better to replace the spare part.

Advice. Sometimes unscrupulous or ignorant auto mechanics damage the ring when repairing the suspension, or even throw it away completely. When picking up your car from a mechanic, always check that this important part is present.

In the case when there is no voltage in the controller circuit, you should ring this section of the wiring. How to do it:

Find out where the electronic control unit for the hydraulic valves is located. For example, in a Chevrolet Aveo it is located behind the brake fluid reservoir, and in a Renault Megane it is located on the side of the alternator drive belt.
Remove the block from the ECU and clean the contacts. Find the pinout of the wires or track them by color.
Place a shorting jumper on the block located near the wheel. Test the circuit with an ohmmeter or a regular light bulb with a battery.

The easiest way to find the ECU if there is no documentation for the car is to follow the brake pipes leading to the hydraulic unit.
The latter stands next to the controller or is connected to it by a bundle of wires. If an open circuit is detected, you will have to look for the defect along the entire line in order to eliminate it. The work is quite complex, so it should be entrusted to an experienced auto electrician.

Using a laptop as an oscilloscope

From a technical point of view, professionals consider using an oscilloscope to be the most correct method for checking ABS sensors. However, the device is expensive, and it makes no sense to purchase it just to test sensors. Well, if you have a laptop, then using it as an oscilloscope is quite simple. First, we make a measuring cord to connect the sensor connector to the microphone input. To do this, you will need a 3.5 mm mini jack plug, two resistors and a couple of pieces of wire of a suitable length. The cash costs for purchasing the necessary components will not exceed 50 rubles. We solder the wires to the contacts of the mini-jack, and install a resistive divider in the gap (to protect the sound card) according to the diagram below.

Then everything is simple:

We install a special Oscilloscope program on the laptop (for example, Winscope or Avangard).
We connect the wires to the ABS sensor connector, and the plug to the microphone input.
Rotate the wheel hub.
If the sensor is working properly, we see a clear sinusoidal signal on the screen.

On a note! If you don't have an assistant, it will be very difficult to rotate the wheel and watch the laptop screen at the same time. For convenience, we recommend using the recording function. By turning on the playback mode (after performing the test described above), you will be able to see the test results.

Alternative verification method

When you don't have a multimeter at hand, you can check the ABS sensor in a simpler way. It will work when only one element fails, and not several. Diagnostics is performed as follows:

Disconnect the connector on one wheel sensor. Next, you need to start the engine and drive a few meters.
If the second light on the brake system (or handbrake) malfunctions comes on, then the element being tested is operational. Connect the block and repeat the operation on the next wheel.
If one sensor is broken, the ABS indicator lights up, and if there are two or more sensors, the handbrake lamp lights up. When the second indicator on the panel does not light up, it means that you have disconnected the faulty element.

The method allows you to determine the location of the problem, but not its nature. For a more accurate diagnosis, you need to use a tester with an ohmmeter.

ABS sensors: how to check the ABS system

The ABS anti-lock braking system (ABS) is one of the most common active safety systems on a car. This solution allows you to avoid complete wheel locking during active braking and maintain control over steering.

In fact, the driver gets the opportunity to brake urgently and control the vehicle at the same time. In turn, this makes it possible to go around an obstacle, change the direction of movement of the vehicle in order to avoid serious accidents, etc.

Of course, if ABS lights up on the instrument panel, it is urgent to diagnose and eliminate malfunctions, ABS errors or failures. As practice shows, frequent failures include failure of system sensors. Next we'll look at how to test ABC sensors.

ABS does not work: ABS sensor and checking it

So, ABS diagnostics are necessary if the system itself is clearly malfunctioning, the ABS icon is on on the instrument panel, etc. It is important to understand that the sensor of this system is an important element.

Moreover, if the car has other active safety systems (for example, anti-skid, exchange rate stability system, etc.), in this case, if the ABS sensors malfunction, failures and malfunctions in the operation of these systems also occur.

The easiest way to determine is computer diagnostics. If the car is not old, then it is enough to connect an OBD scanner and quickly determine which sensor does not indicate wheel rotation.

However, it is important to understand that the data is not always accurate and clearly indicates a malfunction of the sensor. It often happens that the ABC sensor is fully functional, but the problem itself lies in the wiring or the device that detects the rotation of the wheel.

For such a test, the multimeter is switched to “diode” mode, since the vast majority of sensors have a protection diode connected in series to the circuit. It turns out that a regular ringing of the sensor may not give a reliable result.

The sensor should be dialed in both directions. As a rule, the resistance of the ABS sensor can be from hundreds of ohms to 2 kiloohms. It is important to understand that ringing the sensor from the connector still does not allow you to determine how the signal passes to the ABS block.

Please note that the wire that connects the sensor connector and the ABS unit can often be damaged. This problem often occurs with rear ABS sensors. The fact is that there are long cables going back (up to 180 cm). Naturally, at such a length the risks of breaks, chafing, creases and other damage increase noticeably.

To check the sensor from the ABS control unit, you need to determine the pinout of the connector. The fact is that the ABS connectors and sensor contacts on different cars are different. To obtain accurate data, they study special technical literature on a specific car model, use resources on the Internet, etc.

Let's move on. In the case when, after checking with a multimeter, the ABS sensor can ring in one or both directions, this does not always accurately indicate complete serviceability. The reason is that the sensor is an inductor coil located in a magnetic core.

Such a coil has a huge number of turns of thin wire. If moisture gets inside the sensor (given its location on the wheel, this is very likely) or corrosion begins, the element may short out. More precisely, its coil closes (interturn short circuits).

So, in such a situation, the winding resistance practically does not change, but the signal still deteriorates. In turn, this leads to a low signal level and actually means failure of the sensor. In other words, not all ABS faults can be quickly detected using a multimeter.

Main types of ABS malfunctions

Sometimes when you press the brakes, a rattling sound occurs, making drivers think that there is something wrong with their vehicle. But this sound is not a sign of a breakdown: cracking can occur while the modulators are operating.

If the ABS fails, then after starting the engine the icon on the panel does not go out, continuing to light all the time.

During the diagnostic process, the following malfunctions may be detected:

An error found during testing is removed by the ABS system itself. This does not mean that the malfunction has been eliminated: simply, either an error occurs in the main controller unit, or there is a break in the sensor wiring.
When the ABS starts, self-diagnosis takes place in normal mode, but then the device turns off spontaneously. Possible causes include poor-quality contacts or their oxidation, a break in the cable responsible for power supply, or a short circuit in the sensor.
After the ABS starts, the self-diagnosis system finds an error, but still works. In most cases, this indicates a break in the sensor, as a result of which information about the wheel speed begins to be transmitted from another device. The cause of the malfunction may also be a difference in tire pressure: if one tire is flat, it will work slower. A similar situation occurs when installing tires with different treads.
ABS doesn't work at all. The most likely causes will be a break, a heavily worn wheel bearing, or rotor play. To troubleshoot the problem, you should first check the play and condition of the rotor. If chips are found, the element should be replaced. Next - check the wires suitable for the device. If this measure does not lead to the desired result, then the whole problem is in the electronics - in this case, you need to use the diagnostic system to find out the error code to eliminate it.

If replacing the ABS sensor does not produce results

Having considered the available ways to check the ABS, it may seem that it is enough to identify the problematic sensor and replace it. Replacing the wiring may also seem like a solution.

However, in reality it is not so simple. Often, car enthusiasts are faced with the fact that even after replacing the ABS sensor, the system still does not work. By the way, this also happens in cases where the ABS was working normally, but after replacing the hub or wheel bearings the ABS light comes on.

So, the reason in this case is not the sensor at all. Often the culprit is the way the signal is generated from the wheel rotation sensor. More precisely, in the case when the inducing element is the comb ring on the hub (ABS ring). The end part of the sensor itself is located near the comb, which is made of soft magnetic material.

The gap between them is minimal, only from 0.2 to 0.8 millimeters. If dirt or stones adhere to this area, this will lead to a violation of the gap, displacement of the sensor, and destruction of the tip. Naturally, the signal will become weak. Also, the comb itself may become clogged, which causes failures.

Given this feature, before installing a new sensor, you must first check the gap and clean the comb with a solvent. When finished, check the gap size with a feeler gauge. It is not allowed to increase the gap by more than 1 mm. It is also important to inspect the elements for possible damage.

Let us also add that the inducing element on some cars can be implemented in the form of a rubber ring or magnetic tape. There are magnetic plates inside the ring. It happens that during in-line repairs this ring is simply not installed. Naturally, the ABS system will not work without them.

As for the tape, it is easy to damage. This means that you need to work carefully, since if the belt is damaged, the ABS sensor will not work properly. It is also important to ensure that when replacing the wheel bearing, an element with an inducing ring is installed in the case where exactly such a design is provided on the car.