Diagnostic Trouble Code P0504 stands for mismatch of signals from sensors 1 and 2 brake pedal or Brake Switch A/B Correlation. Appears when the ECU receives conflicting information about the current position of the brake pedal.
Most often, error P0504 is recorded in Lada (Kalina, Granta, Priora, Vesta, Largus), Datsun (On-DO, mi-DO), Renault (Logan, Duster), Toyota (Corolla, Land Cruiser Prado) and other models, in in which this information is transmitted to the controller from the four-pin brake light switch.
We will tell you why error P0504 occurs and how to find and eliminate the cause of discrepancies in brake sensor signals in this article.
Symptoms and Conditions for DTC P0504 Appearance
The formation of DTC P0504 is caused by the receipt of certain signals into the electronic control unit from the light limit switch , also known as the “frog”. In a number of cars, in particular Lada models with an electronic accelerator pedal, two pairs of contacts are combined in its body: a normally closed one for the brake pedal position and a normally open one for the brake light circuit. When the pedal is pressed, the first contact opens and the second contact closes.
Information about the state of both contacts is sent to the ECU. If their values do not correspond to each other, for example, both contacts are closed or open, or simultaneously with the information about the brake pedal being pressed, the accelerator pedal is pressed, error P0504 occurs .
Since this algorithm ensures safe operation of the vehicle, if the E-gas system malfunctions, if the signals from the brake and accelerator pedal position sensors diverge multiple times, the engine may go into emergency operation mode .
Therefore, together with error code P0504, certain symptoms may appear:
Decoding error P0504 in the diagnostic program
- The brake light lights up constantly or does not light up when the brake pedal is pressed.
- Cruise control does not activate.
- The dynamics deteriorate, the engine speed does not rise above 1250–1500 per minute and/or drops to idle during acceleration, the engine stalls or does not start.
- On cars with automatic transmission, problems with changing the position of the selector may occur.
- The Check Engine light on the dashboard lights up (usually when the error is detected multiple times).
The set of symptoms directly depends on the nature of the malfunction, the logic of the ECU and the design features of a particular model. In some cases, the malfunction may not reveal itself as anything other than an error code in the memory.
Which one to buy
Experts and service workshop specialists recommend purchasing an original brake sensor. It is of better quality and lasts longer.
Table 1. Price of brake pedal position sensor
| Manufacturer | Code | Cost, rub. |
| AvtoVAZ | 11183720010 | 170 |
| Avar | 2113720 | 180 |
| AMY | 11183720010 | 95 |
Before changing the “frog”, you can “ring” it with a tester to make sure the part is working.
Reasons for mismatch of brake sensor signals and their elimination
In most cases, error P0504 occurs due to a malfunction of the brake light limit switch or its incorrect adjustment (if required). However, failure is also possible if non-standard lamps are installed in the rear lights. The main reasons for mismatch of brake sensor signals and methods for eliminating them are discussed in the table.
| Causes and solutions to error P0504 | ||
| Faulty element | Reason for failure | How to fix |
| Stop light limit switch (“frog”) | Incorrect adjustment | Adjust the position so that the rod is completely recessed into the body when the pedal is released. |
| Spring is weakened or broken | Replace the spring or change the sensor itself | |
| Contacts are burnt or oxidized | Clean the contact plates with sandpaper or a file, or completely replace the end switch | |
| Brake lamps | Burnt out filament | Replace lamp |
| Installed non-standard lamps with lower resistance, for example, LED | Add a resistor to the circuit, replace with lamps with blende or standard ones | |
| Fuse | Brake light circuit fuse blown | Replace the fuse, if it blows again, check the circuit for short circuit |
| Circuit between limit switch, ECU, brake lights and battery | Broken wires, damaged insulation or contact terminals | Visually check the integrity of the wires and contacts, test the wiring with a tester or test lamp |
| ECU | Damage to contacts, failure of elements on the controller board | Replace contacts and faulty components |
After eliminating the cause of the malfunction, it is necessary to reset error code P0504 using a diagnostic scanner and a special application, otherwise the engine may continue to operate in emergency mode.
Bypass Brake Pad Sensor
Many BMW owners choose to bypass (remove) the brake wear sensor by removing the sensor and installing a clip, or by cutting the sensor wire, exposing the wires, and splicing them together.
This is called shorting the wire and emulates a "good" sensor, but is not recommended.
Attention
It is not recommended to permanently disable the BMW brake pad wear sensor. If you bypass the brake pad wear sensor, you will NOT know when your brakes need to be replaced. Your brake pads will wear completely until they reach the metal part, at which point you will have metal to metal contact. Not only will your braking be reduced, but you will also hear grinding noises and your rotors will be damaged and require replacement.
Diagnostic procedure when error P0504 appears
To carry out some diagnostic operations when error P0504 appears, a multimeter or test lamp . If you do not have an assistant to check the operation of the limit switch and the condition of the brake lamps, you can drive up to the wall so that the brake lights are visible in the mirrors.
- Check the brake lights by pressing and releasing the brake pedal several times. The lamps should light up when the brake pedal is depressed 2–3 cm and go out when released. Flashing or flickering indicates poor contact, while intermittent failure indicates incorrect adjustment or wear of the limit switch.
- If the lamps do not illuminate when the pedal is depressed, check that the brake light circuit fuse has not blown.
- Inspect the limit switch connector, make sure it is fixed and there is no external damage.
- Check the brake light limit switch and its adjustment. The verification procedure is discussed in detail in the next section.
- Check the power supply to the sensor using a multimeter or test lamp. One of the terminals must be supplied with 12 V power at all times. Use the vehicle's electrical diagram to determine the appropriate terminal. If there is no power, check the corresponding circuit in sequence.
- If there is power and the sensor is working, check the receipt of signals when the pedal is pressed and released to the corresponding contacts of the computer using a multimeter. Their presence indicates a controller malfunction.
If error P0504 appears after replacing brake light bulbs with LED ones, first of all try installing back the standard halogen ones. Most likely this is the problem.
End switch connection diagram, click to enlarge
Solving the problem through the use of alternative spare parts
Since domestic spare parts do not save the situation, you can resort to using others, namely the brake light switch (FACET 7.1126) for Volkswagens. Such a switch is slightly more expensive than a Lada Granta brake pedal sensor, namely 560 rubles. The device is of a similar type and has:
• threaded leg with a similar diameter of 12 mm.
The only thing you need to use FACET 7.1126 is a terminal adapter.
Checking, repairing and adjusting the brake light switch on cars of different brands
Inside the four-pin brake switch there are two pairs of contacts, the state of which depends on the position of the rod: when fully recessed and fully extended, one pair is always closed - the resistance is close to zero, the other is open - the resistance is several kOhms or more. If for some reason the contact group does not work properly, error P0504 occurs.
Checking the brake light switch
Checking the brake light switch comes down to testing the terminals of a pair of contacts in the normal position - with the rod extended and when it is retracted, simulating pressing the brake pedal. The normal state of the contacts of a working switch for some popular models is shown in the table below.
| Model | Contact status | |
| The rod is recessed | The rod is extended | |
| Toyota Rav4 | 3–4 closed 1–2 open | 3–4 open 1–2 closed |
| Lada (Priora, Kalina and Granta, 4x4) Datsun (on-DO, mi-DO) Gazelle Next, Business | 1–4 open 2–3 closed | 1–4 closed 2–3 open |
| Lada (Largus, Vesta, XRAY)Renault (Logan, Duster) | 3–4 open 1–2 closed | 3–4 closed 1–2 open |
If the test shows that the contacts close and open properly, error P0504 may be due to either incorrect adjustment of the brake light switch (not required on all models) or faulty wiring and other reasons listed above. If the multimeter readings do not match the parameters of a working switch, it must be replaced or repaired.
Repair of brake pedal limit switch
Diagnostics and repair of brake light switch: video
The two main reasons for the failure of the brake light limit switch are oxidized or burnt contacts and a broken or weakened spring. An indirect sign of the second problem is a small stroke of the rod compared to a good one or its free motion.
For repairs, the limit switch must be dismantled. To do this, first of all, disconnect the connector by releasing the latch. In some cars, for example, Lada Kalina and Granta, this requires unscrewing the fastening nut, in others, for example, Lada Largus and Vesta, it is enough to turn its body counterclockwise 90 degrees and remove it from the hole.
Next, you should disassemble the sensor housing, which is secured with latches, and then inspect the condition of the spring and contacts. Oxidized or burnt contacts can be cleaned with sandpaper and treated with a degreaser. The broken spring needs to be replaced with a new one of the same length (for the switch 1118-3720010 installed on Lada cars, a spring with a diameter and height of 6–8 mm is suitable), and you can try to stretch the weakened one, but this will only help for a while.
Repairing the brake pedal end switch is more of a temporary measure in case it was not possible to quickly find and purchase a replacement part. Usually, soon the restored switch begins to work incorrectly again. Therefore, if possible, it is better to install a new switch immediately.
Replacing and adjusting the limit switch: video
instructions
- Determine whether you are replacing the front or rear brake pad wear sensor.
- Raise the car and remove the wheel. When replacing the front brake pad sensor, lift the driver's side wheel. When replacing the rear brake pad sensor, lift the passenger's side wheel. Remove the wheel from the car.
- Locate the brake pad wear sensor on the brake pad.
- Use a flat head screwdriver to remove the old sensor.
- Disconnect the sensor from the brake caliper release valve.
- Disconnect the sensor wire from the rack bracket by pulling it out of the bracket.
- Open the black box attached to the wheel well. Inside you will find a connector.
- Pull the connector out of the box. Press the release tab on the connector and separate the wires.
- Install the new sensor in reverse order.
Handbrake lever limit switch Lada Kalina / Granta / Priora / Vesta, Datsun
- 120 rub. /Thing
Product data
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Handbrake lever end cap for Lada Kalina / Granta / Datsun.
The limit switch is also used as a glove compartment lighting switch in Lada Vesta cars.
Product characteristics
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