Fault code P0504 – brake switch “A”/”B” correlation

Fault code P0504 is called “Brake Switch “A”/”B” Correlation” but in different programs it may be called differently. This fault designation applies to all vehicles equipped with OBD-II.

Technical description and explained code P0504

This diagnostic trouble code (DTC) is a generic transmission code. Error P0504 is considered a general code because it applies to all makes and models of vehicles. Although the specific repair steps may vary slightly depending on the model.

Fault code P0504 – brake switch

Your vehicle’s transmission control module (TCM) is transmitting code P0504 in response to a recognized failure in the brake light circuit. The vehicle’s computer monitors all circuits for such abnormalities, such as no voltage or out of range condition.

The brake light switch is tied to several circuits, each of which can lead to a dangerous situation. The stop light switch itself consists of two signal outputs, and if the switch malfunctions, the problem is detected and this code appears.

This is not a costly breakdown in terms of the cost of parts or the labor involved in replacing it. But for your safety, it is necessary to make repairs as soon as possible.

Symptoms of vehicle malfunctions

The main signal that an error P0504 has occurred is the Malfunction Indicator Lamp (MIL) is also known as the CheckEngine Light.

It can also be warning signs such as:

  1. The brake lights will either be on continuously or will not come on when the pedal is depressed.
  2. It will be difficult or impossible to move the vehicle.
  3. The vehicle may stall while driving if the brakes are applied.
  4. Cruise control cannot be activated with this problem.

Fault P0504 is not serious, most likely the car will be able to continue driving, but there may be exceptions. Most often the symptoms will include either the brake lights on all the time, or they will not work at all.

Factors that can cause this error code

The error code P0504 can mean that one or more of the following problems have occurred:

  • Short circuit in the brake light switch signal circuit.
  • Failure in the brake light switch, failure of which is due to wear and tear.
  • Problem with the fuses, sometimes failing due to moisture in the circuit or brake light burnout.
  • If the wiring harness, or more specifically the connectors, are loose or disconnected, this will cause a correlation problem between the switch and the ECU.
  • And, of course, the ECU itself could have malfunctioned.

How to fix or reset OBD-2 code P0504

Some suggested steps for troubleshooting and fix the error code P0504:

  1. With the help of an assistant, check the brake lights. Make sure they work by turning them on and off and that the bulbs are okay.
  2. If the brake lights are on continuously, the brake light switch is either not adjusting properly or is defective. The same is true if the bulbs are faulty. Pull the driver’s seat back and look under the dashboard. Squeeze the tabs on the electrical connector located on the brake light switch and remove the connector.
  3. Use a voltmeter to check the voltage on the red wire in the connector. Place the black wire on the ground and the red wire on the red wire terminal. The voltmeter should show 12 volts, if not, it is worth checking the wiring to the fuse box.
  4. Connect the connector to the switch and measure the white wire with the pedal depressed. You should have 12 volts with the pedal depressed and no voltage with the pedal released. If there is no voltage, replace the switch. If there is voltage on the white wire with the pedal released, also replace the switch.
  5. If the switch is adjustable, check it. The switch should be in good contact with the brake pedal lever and fully depressed.
  6. If the brake lights work fine, but the code is still there, check the other wires on the brake light switch. Remove the connector and check the remaining wires for power. Make a note of the location of the power wires and replace the connector. Tape the rear wire next to the power wire while the pedal is depressed. If no power is present, replace the switch.
  7. If the power was on in the last test when the pedal was depressed, the switch is okay. There is a problem with the connection to the control box or with the vehicle’s control box itself.
  8. Connect the control unit and the brake pedal sensor through the ground. If the voltmeter shows 12 volts, the control unit is faulty. If there was little or no voltage, replace or repair the harness from the control unit to the sensor.

Diagnose and repair of problems

The main problem is considered to be a discrepancy between the data in the PCM and the brake pedal sensor. Therefore, let’s take a closer look and describe some suggested steps for troubleshooting and correcting error code P0504.

The brake light switch is located under the dashboard at the top of the brake pedal lever. The brake booster raises the pedal to its fully extended position. The brake light switch is mounted on the crossbar support bracket directly behind the brake pedal mounting bracket.

The only way to access the switch is to move the front seat back, lie back and look up under the dash. You will see the bracket with the switch, near the top of the brake pedal lever. The switch will have four or six wires.

The switch rests on the bracket so that its drive rod is in contact with the brake pedal lever when the pedal is fully extended. At this point, the switch is depressed on the brake pedal lever, disconnecting the voltage supply.

When the brake pedal is depressed, the lever extends to engage the switch and turn on the brake lights. When the pedal is released, the lever pulls the bar out again, turning off the brake lights.

Therefore, it is very likely that replacing this sensor will eliminate the problems with error P0504.

On which vehicles does this problem occur most frequently

Fault code P0504 can occur on different vehicles but there are statistics on which brands this occurs most often. Here is a list of some of them:

  • Chery (Fora)
  • Chevrolet (Captiva, Epica)
  • Citroen (C4)
  • Datsun (on-DO)
  • Fiat (Doblo, Ducato)
  • Ford (Focus, Fusion, Kuga, Transit)
  • Hyundai (Grand Starex, Santa Fe, Solaris, Starex, i30)
  • Kia (Ceed, Rio, Sorento, Sportage)
  • Land Rover (Freelander, Range Rover)
  • Lexus (GS300)
  • Lifan (X60)
  • Nissan (Pathfinder)
  • Opel
  • Peugeot (308, Boxer)
  • Toyota (Auris, Avensis, Corolla, Land Cruiser, Prado, RAV4)
  • Volvo
  • GAZelle (Business, Next)
  • LADA (Granta, Kalina, Largus, Niva, Priora, Vesta)
  • UAZ (Hanter, Patriot)
  • VAZ (2113, 2114, 2115)

Fault code P0504 can sometimes be found with other errors. The most common are the following: P0016, P0019, P0098, P0121, P0171, P0422, P0432, P0455, P0500, P0571, P0700, P0716, P0732, P0733, P0734, P0746, P0842, P2714, C1241, U0405.

Video

Rate article
AutoNevod | Technical description of OBD-2 car faults and their solution
Add a comment