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.