P0504 OBD II Trouble Code Brake Switch A/B Correlation DTC

Symptoms of P0504 OBD II Trouble Code

  • 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

Common Causes of P0504 OBD II Trouble Code

  • 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.