What are the common causes of P0504?

Faulty brake light switch. Misadjusted brake pedal switch. Shorted or open switch wiring. Brake pedal travel sensor out of range. Faulty PCM.

Observe brake pedal switch states on a scan tool. Verify brake lights operate correctly. Check switch adjustment at the pedal. Test switch continuity across pedal travel. Replace the brake switch and verify A/B correlation clears.

P0504

Brake Switch A/B Correlation

System: Speed and idle control (P code)
Lamp: Check Engine Light
Category: Powertrain - Computer and Auxiliary Controls

What it means

P0504 means Brake Switch A/B Correlation.

Where it lives

For P0504, the description names the switch as the part involved.

Check these first

Faulty brake light switch
Misadjusted brake pedal switch
Shorted or open switch wiring
Brake pedal travel sensor out of range
Faulty PCM

What to do next

Observe brake pedal switch states on a scan tool
Verify brake lights operate correctly
Check switch adjustment at the pedal
Test switch continuity across pedal travel
Replace the brake switch and verify A/B correlation clears

Look up another code

Code or symptom

Enter a full code or a symptom. Press / to search. How to read a code

Type a code above, or start from a symptom or a common code.

Updated

Generic SAE J2012 definition. Last updated 2026-08-30.