Brake Switch Correlation Failure
The P0504 code indicates a correlation fault between the brake pedal position sensor and the brake light switch. The powertrain control module (PCM) detects that the signals from these two sensors do not match, suggesting a mechanical or electrical issue. This can affect cruise control, shift interlock, and brake light operation.
1. Most Common Causes
- Faulty brake light switch
- Misadjusted brake pedal position sensor
- Wiring or connector issues in the brake switch circuit
- Blown brake light fuse
2. Symptoms You Will Notice
- Brake lights stay on or do not illuminate
- Cruise control inoperative
- Shift interlock malfunction
- Check Engine Light illuminated
3. Step-by-Step Diagnosis
Step 1: Verify brake light operation; check for stuck or non-functional lights.
Step 2: Inspect brake light switch for proper adjustment and continuity.
Step 3: Check wiring and connectors for damage, corrosion, or loose connections.
Step 4: Test brake pedal position sensor signal with a scan tool.
Step 5: Replace faulty components and clear code; test drive to confirm repair.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended because brake lights may malfunction, increasing the risk of rear-end collisions. Cruise control and shift interlock may also fail.
How much does it cost to fix?▼
Typically $50-$150 for parts and labor, depending on the cause. A brake light switch replacement is often under $100.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.