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Generic SAE code Chassis and brakes

C0042: Brake Pedal Position Sensor Circuit "A"

The control unit has detected a fault in the brake pedal position sensor circuit A.

High risk

Have it checked soon. Brake lights, cruise control or brake assistance may be affected.

Short answer · Can I keep driving with C0042?

Usually yes, with care. Brake lights, cruise control or brake assistance may be affected. Have it checked soon.

On this page

What does C0042 mean?

C0042 points to a sensor that measures how far the brake pedal is pressed. Many cars use two signals that are compared with each other.

What the car does when the code is set

The brake warning light may come on, and brake assistance or ABS functions may be limited.

How the system works

Modern brakes use sensors for fluid level, pedal position, pressure and pad wear. The brake control unit uses them for ABS, brake assistance and warnings.

CChassis
0Generic code (SAE)
0Chassis and brakes
42Specific fault

Common symptoms

Brake System Warning LightRed lightCritical riskABS Warning LightAmber lightHigh riskBrake Pad Wear WarningAmber lightHigh riskSoft Or Spongy Brake PedalStop and checkCritical riskHard Brake PedalStop and checkCritical riskBrake Fluid LeakStop and checkCritical risk

Possible causes

Listed without ranking. The cause on your car depends on make, engine and mileage — see the maker notes below.

  1. Low brake fluid levelWorn pads or a leak lower the level in the reservoir.
  2. Faulty sensorPressure, travel or level sensors can fail internally.
  3. Wiring or connector faultDamaged wires or corroded plugs give wrong signals.
  4. Air or moisture in the brake fluidOld fluid or a leak changes how the system behaves.
  5. Brake booster or hydraulic unit faultPossible once fluid, sensors and wiring have been checked.

How it is diagnosed

  1. Check the brake fluid levelWith the car level, the fluid should sit between MIN and MAX.If the level is low or the pedal feels soft, do not drive; have the car recovered.
  2. Look for leaksCheck behind each wheel and around the master cylinder for fluid.
  3. Check the padsWorn pads lower the fluid level and may trigger wear warnings.
  4. Read live dataA workshop compares sensor values with the pedal at rest and pressed.

Questions about C0042

Can this code affect the brake lights?

Yes. On some cars the pedal sensor also controls the brake lights; check them.

Is a brake system code an emergency?

It can be. If the brake warning light is red or the pedal feels different, stop driving and have the car checked.

Terms on this page

Brake FluidBrake Pressure SensorBrake BoosterABS Module (Hydraulic Unit)