C0040Brake Pedal Switch A
- Generic OBD-II code · Chassis
- Can trigger limp mode
- How the car detects it
- C0040 reports a fault on brake pedal switch A, the first of two switch signals that tell the brake, engine and transmission modules the pedal is pressed. Mazda defines C0040:24 as a circuit malfunction of brake switch signal no. 1; on the 2024 CX-90 it appears with P0504 and a push button start warning, and service alert SA-062-23 cures it by moving the switch one adjustment notch. Ford sees C0040 with P0504 on 2020-2022 F-Super Duty trucks that cannot be moved out of park, pointing to corrosion inside the battery junction box or a damaged shift-interlock circuit. Typical effects are stop lamps that stay lit (Ford TSB 22-2044), a start system warning and a shift interlock that will not release. Older GM vehicles use C0040 for a wheel speed sensor circuit in their own scheme.
- What you may notice
- Stop lamps stay on or do not light
- Vehicle will not shift out of park
- Push button start malfunction warning (Mazda)
- Likely causes
- LikelyBrake switch out of adjustment (Mazda SA-062-23)
- PossibleWater or corrosion in the battery junction box (Ford TSB 22-2044)
- PossibleDamaged switch or shift-interlock wiring
- RareBrake switch failed internally
- Repair
- Easy · Often possible to do yourself.Typical cost: €20 – €180
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.