What does it mean?
C1242 is a Chassis (ABS, traction control, steering) fault code. It indicates: Abnormality In G And Yaw Rate Sensor (Abnormality In Longitudinal G Sensor Output Signal) .
Symptoms
- Stability, traction and ABS lamps on, with the stability system switched off
- Hill-hold and hill descent functions unavailable
- Stability control intervening on a flat, straight road
- Longitudinal G reading on the scan tool not at zero with the vehicle level and stationary
- Fault appearing after carpet, console, seat or floor pan work, or after an impact
Likely causes
- Internal failure of the sensor element, giving a drifting, noisy or offset output
- Sensor bracket loose, bent or the unit refitted in the wrong orientation after interior or floor work
- Calibration never performed after replacing the sensor, the stability module or after alignment
- Corroded or partly unplugged connector, often after water has entered the cabin floor
- Open, shorted or high resistance supply, ground or signal wire to the sensor
- Accident damage to the mounting area, changing the sensor angle relative to the vehicle
- Low system voltage or a communication fault on the bus carrying the sensor data
How to fix it
- Park on a level surface and read the longitudinal G value at rest; it should sit near zero
- Compare the lateral G and yaw rate values at the same time to see whether one channel alone is wrong
- Check the sensor is tight, correctly oriented and that its bracket is not bent or corroded
- Inspect the connector for moisture and corrosion and check supply, ground and signal at the plug
- Look for water ingress under the carpet where the sensor is mounted
- Perform the sensor calibration routine and repeat a short road test with gentle braking and acceleration
- Replace the sensor if the value still drifts or does not respond, and recalibrate afterwards