Chassis, generic

C0040 Brake Pedal Switch A

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

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.

Likely causes

Brake switch out of adjustment (Mazda SA-062-23)
Water or corrosion in the battery junction box (Ford TSB 22-2044)
Damaged switch or shift-interlock wiring
Brake switch failed internally

Symptoms

  • Stop lamps stay on or do not light
  • Vehicle will not shift out of park
  • Push button start malfunction warning (Mazda)

Repair estimate

DifficultyEasyDIY possible
Parts and labour€20–180
Time0.3–1 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

brake pedal switch a

Related codes

C0041C0042C0043

References: static.nhtsa.gov, static.nhtsa.gov, static.nhtsa.gov, rosap.ntl.bts.gov.