C0042 Moderate Generic / SAE

C0042: Brake Pedal Position Sensor Circuit A

What to do

Ordinary braking is unaffected. What may be reduced is emergency brake assistance, and on a hybrid or electric car the smoothness of the changeover between regenerative and friction braking — you might notice the pedal feeling slightly different. Worth getting fixed rather than living with.

What this code means

Brake pedal position sensor circuit A has a fault.

A switch says whether the pedal is pressed. A position sensor says how far — and modern braking needs the difference.

Regenerative braking is the clearest reason. In a hybrid or electric car, gentle braking is done by the motor generating current back into the battery, and the friction brakes are blended in as demand rises. Blending needs a number, not a yes/no, and it needs it accurately enough that the handover is invisible to the driver.

Emergency brake assist is the other. The system watches how fast the pedal moves: a stab at the pedal is read as panic, and full pressure is applied before the driver's own effort reaches it. A rate cannot be measured from a switch.

Circuit A and circuit B are the two halves of one sensor, reported separately so the module can tell a plausible-but-wrong reading from an obviously dead one. Two circuits disagreeing is a sensor fault; one open is usually wiring.

Note the designator convention here differs from its neighbours. These codes quote Circuit A and Circuit B where the switches at C0040 and C0041 quote a bare letter — the same lettering scheme written two ways within a few numbers.

Likely causes

Start here

Faulty brake pedal position sensor · specialist
Corroded or loose connector · specialist
Damaged wiring harness · specialist
Open circuit in sensor wiring · specialist

Less common

Faulty stability control module · specialist

Symptoms

Components involved

Information, not instruction

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Community experience

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