P0504 2011 Ford Fusion Code - Brake Switch Circuit 'A' / 'B' Correlation

P0504 indicates a correlation issue between the two circuits of the brake switch, which monitor the brake pedal's position and operation.

Symptoms may include the brake lights not working, the cruise control malfunctioning, ABS or traction control warnings, and erratic braking performance.

The code can be caused by a faulty brake light switch, corroded or damaged wiring, a misaligned brake pedal switch, or a malfunction in the vehicle's electronic control module.

Start by inspecting and replacing the brake light switch if necessary. Check for damaged wiring or poor connections and repair them. If the issue persists, further diagnosis may be needed.

Driving with this code is not recommended, as it can affect brake light functionality and safety features like ABS and cruise control.

The cost varies, but replacing a brake light switch typically costs $50–$150, including parts and labor. Wiring repairs might increase this cost.

Use an OBDII scanner to confirm the code, then inspect the brake light switch and its wiring for damage, corrosion, or misalignment. Test the switch with a multimeter if needed.

No, a dead brake light bulb is unlikely to cause this code. The issue is more related to the brake switch and its circuits.

Clearing the code may temporarily turn off the check engine light, but the underlying problem must be addressed to prevent the code from returning.

While rare, a faulty ABS module could indirectly contribute to this code if it misinterprets brake switch signals. However, the brake light switch and wiring are more common culprits.