Brake Switch Correlation Failure
The P0504 code indicates a correlation fault between the brake pedal position switch and the brake light switch. The powertrain control module (PCM) detects that the signals from these two switches do not match, suggesting a mechanical or electrical issue. This can affect cruise control, shift interlock, and brake light operation.
01. Most Common Causes
- Faulty brake light switch
- Misadjusted brake pedal position sensor
- Wiring or connector issues in brake switch circuit
- Blown brake light fuse
02. Symptoms You Will Notice
- Brake lights stay on or don't illuminate
- Cruise control inoperative
- Check Engine Light illuminated
- Shift interlock malfunction
03. Step-by-Step Diagnosis
Step 1: Use a scan tool to verify the code and check freeze frame data.
Step 2: Visually inspect brake light operation and check for blown fuses.
Step 3: Test brake switch continuity and adjustment with a multimeter.
Step 4: Inspect wiring and connectors for damage or corrosion.
04. Commonly Affected Makes
05. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended as brake lights may malfunction, increasing risk of rear-end collision. Also, cruise control and shift interlock may not work.
How much does it cost to fix?▼
Typically $50-$150 for parts and labor, depending on the cause. A brake switch replacement is often under $100.