P0504 - BRAKE SWITCH “A” /” B” CORRELATION

POST UPDATED IN October, 2021

Description of DTC code P0504 Generic

The vehicle’s computer controls all circuits looking for problems in one of them, such as voltage deficiency or an out of range position.

If the Power Train Control Module (PCM) has set the DTC code P0504 OBDII it is because it has detected a recognized fault in the brake light circuit. Because the light brake switch is connected to several circuits, there are situations of risk. This switch has two signal outputs and if one of them is malfunctioning, this diagnostic code is established. This code must be attended in the shortest time possible for the safety of the vehicle.

Symptoms of fault code P0504 Generic

  • MIL light (Malfunction indicator) lit.
  • While the brake pedal is held down, the brake light does not come on.
  • After stopping pressing the brake pedal light, the brake lights remain on.

Causes of OBD2 P0504 Generic

The reasons why the diagnostic code P0504 OBD2 can be set are:

  • Brake light switch is worn out.
  • There is probably moisture in the brake light fuse.
  • Faulty brake light bulb, perhaps due to the presence of water.
  • Defective cables or connectors in the middle of the switch and the Powertrain Control Module (PCM).

Possible solutions of the DTC code P0504 Generic

To solve the problems that the fault code P0504 OBD2 entails, you must do the following:

  • If the lights of the brake are permanently on, it is possible that the brake switch is defective. It also applies if the lights do not work. So, check under the board, look for the electrical connector tabs to make sure they are adjusted correctly.
  • If the above has not solved the problem, with a voltmeter, check the voltage on the red wire of the connector. Then, you must put the black wire to a good ground and the red wire to the corresponding terminal. It must have a reading of 12 volts. Otherwise, check the cables in the fuse holder. Change any electrical component that is defective.
  • Put back the brake light bulb.
  • Replace the brake light fuse.
  • Change the brake switch.

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