OBD-II code · Powertrain (generic)
P0504 Brake Switch "A"/"B" Correlation
Modern vehicles use two redundant brake switch signals (often one normally-open and one normally-closed). When the two signals disagree, this code is set; common causes include a misadjusted switch, internal switch failure, or wiring fault.
Is it safe to drive with P0504?
Usually safe to drive in the short term. Get it diagnosed when convenient, sooner if the car drives differently.
Common causes
- Most likelyBrake switch misadjusted
- PossibleBrake switch internal fault
Repair at a glance
- Difficulty
- Easy
- DIY friendly
- Often, with basic tools
- Typical labour
- 0.2–1 h
- Emissions test
- Usually unaffected
- Parts involved
- Brake Light Switch, Brake Switch Wiring
Related codes
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.