What does it mean?
C1240 is a Chassis (ABS, traction control, steering) fault code. It indicates: Steering Angle Sensor Angle Overtravel Performance .
Symptoms
- Stability and ABS warning lamps on, with the stability system switched off
- Angle shown on the scan tool clearly larger than the steering can physically reach
- Fault appearing right after steering wheel, clock spring, rack or column work
- Adaptive lighting, park assist and lane functions inactive
- Stability control intervening in the wrong direction during cornering
Likely causes
- Zero point calibration lost or never performed after a battery disconnect or module replacement
- Sensor internally miscounting, so the angle keeps climbing past the real lock position
- Clock spring assembled off centre, leaving the sensor working outside its intended range
- Sensor rotated past its range while the column, rack or steering wheel was removed
- Worn column coupling or intermediate shaft letting the sensor lag or overshoot the road wheels
- Corrupted angle data on the network, or dropouts that make the module lose count
- Low system voltage disturbing the sensor during operation
How to fix it
- Read the live angle with the wheel centred and again at each full lock, and compare with the mechanical range of the steering
- Confirm the clock spring is centred correctly and the steering wheel is fitted in the right position
- Check the intermediate shaft, coupling and rack mounting for play
- Run the zero point calibration and see whether the sensor accepts it and holds the value
- Look for network errors and check system voltage and the module ground
- Wiggle test the column wiring while graphing the angle to find dropouts
- Replace the sensor, or the clock spring where the sensor is part of it, and recalibrate