P0504Brake Switch A/B Correlation
- Generic OBD-II code · Powertrain
- Can trigger limp mode
- How the car detects it
- The brake pedal switch has two contacts – A usually for the brake lights, B for cruise control and brake information – working in opposite sense, so the module expects opposite states on every brake application. P0504 means they disagree. The signal is used for cruise control cut-off, brake override with electronic throttle, the shift interlock and start-stop. Ford sets it only after more than 25 (petrol) or 40 (diesel) disagreeing brake applications, with the wrench lamp instead of the warning lamp; a NHTSA investigation covers Hyundai brake light switches.
- What you may notice
- Cruise control cannot be switched on
- Brake lights stay on or do not come on
- Selector lever cannot be moved out of P
- Wrench or ESC lamp on
- Likely causes
- LikelyBrake light switch faulty (burnt or corroded contact)
- LikelySwitch misadjusted or retaining clip or stop pad worn
- PossibleWire, connector or brake light fuse faulty
- RareMoisture in fuse or junction boxes
- Repair
- Easy · Often possible to do yourself.Typical cost: €20 – €150
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.