What does it mean?
C1200 is a Chassis (ABS, traction control, steering) fault code. It indicates: Wheel Speed Sensor Front-LH Open/Short .
Symptoms
- ABS, traction and stability control lamps on together and staying on
- ABS does not intervene: the pedal stays firm and a wheel can lock under hard braking
- Front left wheel speed reads a flat zero on the scan tool while the other wheels track road speed
- Speedometer, cruise control or hill-start assist may misbehave on vehicles that use this signal
- The fault can come and go over bumps or full steering lock before it becomes permanent
Likely causes
- Broken conductor in the sensor lead where it flexes with the steering and suspension between the knuckle and the inner wing
- Sensor winding open or shorted internally after heat and vibration
- Wire chafed against the strut, the brake hose bracket or the wheel arch liner, shorting to the body
- Corroded or waterlogged connector behind the arch liner, giving a very high or a bridged resistance
- Connector left unlatched or a terminal pushed back after brake, hub or driveshaft work
- Damage to the lead from a stone strike, a snow chain or rodent activity
- Fault in the ABS module input circuit for that channel
How to fix it
- Read live wheel speed for all four wheels and roll the car slowly to confirm which channel has dropped out
- Inspect the sensor lead at the front left corner along its whole length, especially where it follows the strut and passes the knuckle
- Unplug the connector, look for water and green corrosion, and check that the terminals are tight and fully latched
- Measure the sensor circuit at the module side: an open reads very high resistance, a short reads near zero or shows voltage present where it should not be
- Check the sensor circuit for a short to ground and to battery voltage with the module unplugged
- With live data running, wiggle the harness at every clip and flex point to find a break inside the insulation
- Repair the damaged wiring or connector, then replace the sensor if the circuit measures correctly and the sensor itself is out of specification