What does it mean?
C1238 is a Chassis (ABS, traction control, steering) fault code. It indicates: Wheel Speed Sensor Supply Voltage Circuit Intermittent . This is a standardised OBD-II code. The technical definition is the same regardless of the make or model of vehicle, although specific causes and symptoms can vary between vehicles.
Symptoms
- Several wheel speed sensor codes stored at the same time
- ABS and stability lamps coming on and going off again on the same drive
- ABS dropping out over bumps, in heavy rain or after a wash
- All four wheel speed readings falling to zero briefly on the scan tool
- Warning lamps sometimes clearing on the next start, with the fault stored as intermittent
Likely causes
- Chafed or partly broken supply wire in the sensor harness, opening as the vehicle moves
- Corroded common splice where the supply branches out to several sensors
- One sensor shorted internally, pulling the shared supply down for all of them
- Water in a wheel arch connector or body grommet raising resistance in the supply path
- Loose terminal tension in the ABS module connector on the supply pin
- Poor ABS module ground, so the reference for the supply moves about
- Supply driver inside the ABS module becoming weak with heat
How to fix it
- Measure the sensor supply voltage at each wheel connector with the key on and compare the readings
- Wiggle the harness at each wheel arch, the body grommets and the module connector while watching the voltage
- Unplug one sensor at a time; if the supply recovers, the sensor just removed is loading the circuit
- Inspect the common splice or junction where the supply feeds several sensors
- Voltage drop test the supply and the module ground under load
- Repair or renew the damaged harness section and reseal the connectors
- Replace the shorted sensor, and treat the module supply driver as the last suspect