C0040 code meaning
Brake Pedal Switch A
What C0040 means
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.
C0040 at a glance
- Check engine lightUsually not
- Emissions testNot an emissions code
- Limp modePossible
- Repair difficultyEasy, DIY possible
- Typical labor0.3 to 1 hours
- Clears after repairWhen cleared with a scanner
Symptoms of C0040
- Stop lamps stay on or do not light
- Vehicle will not shift out of park
- Push button start malfunction warning (Mazda)
Common causes of C0040
- Most 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
- Less likelyBrake switch failed internally
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Brake pedal switch a
What each part of C0040 means
| C | Chassis system: brakes, ABS, steering and suspension. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 40 | The exact fault in that area. |
What to do next
- Note C0040 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about C0040
What does C0040 mean?
C0040 means "Brake Pedal Switch A". 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. It is a generic code, so it means the same on every make.
Is it safe to drive with C0040?
Drive gently and only to a workshop. With C0040 the car can go into limp mode (reduced power) to protect itself.
Will C0040 fail an emissions test?
C0040 is not an emissions code, so on its own it usually does not fail an emissions test. Other stored codes or a lit check engine light still can.
How hard is C0040 to fix?
Difficulty: easy. A typical repair takes 0.3 to 1 hours of work. A careful DIY repair is possible with basic tools and a scanner.
Will C0040 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.