What does it mean?
C1206 is a Chassis (ABS, traction control, steering) fault code. It indicates: Wheel Speed Sensor Rear-LH Open/Short .
Symptoms
- ABS, traction and stability control lamps on and remaining lit
- ABS does not operate: the pedal stays hard and the rear can lock and step out during a hard stop
- Rear left wheel speed reads zero in live data while the other three follow road speed
- Stability control cannot brake that rear wheel, so the car feels less settled when braking in a bend
- On some vehicles the electronic parking brake or hill-hold function reports a fault as well
Likely causes
- Sensor lead corroded or broken where it runs along the trailing arm or rear axle beam, exposed to road salt and spray
- Sensor winding open or shorted internally after years of water and heat cycling
- Cable chafed against the axle, a spring seat, the brake pipe or the handbrake cable bracket
- Connector in the rear wheel arch full of water, giving a very high resistance or bridging the two wires
- Wire pinched or cut during earlier brake shoe, handbrake cable or suspension work at the rear
- Rodent damage or a stone strike on the exposed underbody section of the loom
- Fault in the ABS module input circuit for the rear left channel
How to fix it
- Read all four live wheel speeds and roll the car to confirm which channel is dead
- Inspect the rear left sensor lead along the trailing arm and axle, looking for corrosion, chafe marks and previous repairs
- Open the connector in the wheel arch, check for water and corrosion, and confirm the terminals are tight and latched
- Measure the circuit from the ABS module connector for an open or a short, and compare with the opposite rear channel
- Test that circuit for a short to ground and to battery with the module unplugged
- Wiggle the harness with live data running, concentrating on the section that moves with the suspension
- Repair the harness or connector, then replace the sensor if the wiring is proven and the sensor measures out of specification