OBD-II Generic Error Code P0504: How to Fix It

Q: What does error code P0504 mean?

P0504 means the brake switch A and B signals do not match. The computer expects both switches to change state together. A mismatch indicates a faulty switch, adjustment, or wiring issue.

Q: Can I drive with a P0504 code?

You can drive short distances, but problems with brake lights (safety hazard) and cruise control disengagement may occur. It's best to fix it promptly.

Q: How much does it cost to fix P0504?

A brake light switch costs $10-$40, and an OBD2 scanner can be $20-$100. DIY repair is cheap; professional repair may be $100-$200 including labor.

Q: Will P0504 cause my car to fail inspection?

Yes, because it affects brake light operation. Fixing the issue is necessary to pass emissions or safety inspection.

Q: Can I fix P0504 without an OBD2 scanner?

You can replace the switch without a scanner, but you won't be able to clear the code. The code will eventually clear after several drive cycles if fixed, but a scanner is recommended.

Abstract

Error code P0504 means your car's computer detected a mismatch between the two brake pedal position switches. This usually points to a faulty brake light switch, misadjusted pedal, or wiring issue. The problem needs fixing to ensure brake lights work properly and cruise control disengages.