C0040: Right Front Wheel Speed Sensor Circuit (GM)
The ABS module has detected a fault in the right front wheel speed sensor circuit.
High risk
Have it checked soon. ABS and stability control may be off.
Short answer · Can I keep driving with C0040?
Normal braking works, but ABS and stability control may be off. Drive carefully and repair soon.
What does C0040 mean?
C0040 points to the right front wheel speed sensor, its wiring or connector.
Note: this page uses the definition used by General Motors. In the SAE J2012 generic list, C0040 means brake pedal switch A. Other makes may use the code differently; check the description your scanner shows.
What the car does when the code is set
The ABS and stability control warning lights come on and those systems are usually switched off. Cruise control and other functions that use wheel speed may also stop working.
How the system works
Each wheel has a speed sensor that reads a toothed or magnetic ring turning with the wheel. The ABS control module monitors the sensor circuit and signal; a fault in the circuit sets a wheel speed sensor code for that wheel.
Common symptoms
Possible causes
Listed without ranking. The cause on your car depends on make, engine and mileage — see the maker notes below.
- Damaged sensor or wiringThe wire near the wheel is exposed to stones, water and movement.
- Dirt or rust on the sensor or tone ringDebris weakens the signal.
- Damaged tone ring or wheel bearing encoderCracked rings or worn bearings with built-in encoders.
- Connector corrosionWater and salt attack the plug.
- Excess wheel bearing playA worn bearing changes the air gap.
How it is diagnosed
- Note which lights are onABS and stability control lights usually come on together.
- Inspect the sensor and wiringLook for broken, chafed or pulled wires near the wheel.Lift the car only on proper stands, never on the jack alone.
- Compare wheel speeds in live dataAt low speed, all four wheels should show nearly the same value. The one that drops out or differs points to the fault.
- Check the wheel bearingHumming or play can point to a bearing with a damaged encoder.
Questions about C0040
Should both front sensors be replaced?
Not usually; replace the faulty one after checking wiring and the tone ring.
Can I drive with a wheel speed sensor code?
Normal brakes work, but ABS and stability control may be off. Drive carefully, especially in the wet, and have it repaired soon.