What does it mean?
C1202 is a Chassis (ABS, traction control, steering) fault code. It indicates: Wheel Speed Sensor Front-LH Invalid/No Signal .
Symptoms
- ABS, traction and stability control lamps on, generally all at once
- Front left wheel speed stays at zero in live data while the car is moving
- ABS never activates, so the pedal is firm and the wheel can lock in an emergency stop
- Traction and stability control cannot regulate that corner, so wheel spin is not controlled on a slippery surface
- Speed related functions such as cruise control or hill-start assist may be unavailable
Likely causes
- Sensor tip loaded with metallic swarf, rust flakes or brake dust so it cannot read the tone ring
- Cracked, corroded or chipped tone ring, or a ring that has come loose on the hub or driveshaft
- Excessive air gap because the sensor is not seated fully or corrosion has built up behind it in the hub bore
- Sensor dead internally, so the circuit reads within range but produces no pulses
- Damaged sensor lead giving a signal too weak or noisy for the module to use
- Worn wheel bearing letting the hub wander, so the pulses disappear under load
- Wrong sensor or wrong hub fitted, with a tooth count that does not match the module's expectation
How to fix it
- Watch live wheel speeds while rolling the car; the channel that stays at zero while the circuit is intact points at a signal problem rather than a broken wire
- Remove the sensor and inspect the tip and the hub bore for metal debris and rust scale, then clean both thoroughly
- Turn the wheel by hand and inspect the tone ring all the way around for cracks, missing teeth and rust swelling
- Check the sensor seats fully with the correct air gap, and clear any corrosion from the bore before refitting
- Measure the sensor: resistance for a passive type, or supply voltage and switching signal for an active type
- Check wheel bearing play, since a worn bearing can move the ring far enough to kill the signal
- Replace the sensor if it fails its test, or the hub and bearing assembly if the tone ring is damaged, then confirm all four wheel speeds match on a road test