Technical Definition:

Brake Switch A / B Correlation

Trouble Code: P0504
Address: 0x0504
System: Powertrain
Subsystem: Vehicle Speed Control, Idle Controls, and Auxiliary Inputs
Technical Description:

Possible Causes:
  • The most common is the brake light switch whose failure is due to wear.
  • The brake light fuse will fail at times due to moisture in the circuit or burning out the brake light.
  • Brake light bulb failure is another cause many times due to water infiltrating into the lens.
  • The wiring harness, more specifically the connectors are loose or pushed out pins will cause a correlation problem between the switch and PCM.
  • Lastly, the PCM itself could have failed.

Possible Symptoms:
  • The brake lights will either be illuminated continuously or fail to illuminate as the pedal is depressed
  • It will be difficult or impossible to shift out of park
  • The vehicle may stall when the brakes are depressed while a cruising speeds
  • The cruise control will not activate

Possible Solutions:

OBD-II Trouble Code Type:

Diagnostic Step:

Tech Notes:

Specific Makes:

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