What does it mean?
C1234 is a Chassis (ABS, traction control, steering) fault code. It indicates: Wheel Speed Sensor Front RH Tone Ring Missing Tooth Fault .
Symptoms
- ABS and stability lamps that light after driving a short distance rather than at key-on
- Short, unwanted ABS pulse or a brief brake grab at low speed while coming to a stop
- Stability and traction control switched off after the code sets
- Fault clears but returns on the next drive
- Sometimes a rumble or growl from the right front hub if the bearing is also worn
Likely causes
- Chipped, cracked or broken tooth on the right front tone ring
- Corrosion lifting the ring so a tooth is buried in rust scale
- Ring damaged during hub, bearing or drive shaft work, or knocked when refitting the sensor
- Magnetic encoder ring in the bearing seal scored, contaminated by grease or partly demagnetised
- Debris such as a stone chip or metal swarf packed into the tooth gaps
- Incorrect hub or ring fitted with a different tooth count
- Excessive bearing play letting the gap change at one point of the rotation
How to fix it
- Graph the right front wheel speed while driving slowly and look for a regular dip that repeats once per wheel revolution
- Raise the wheel, remove the sensor and rotate the hub by hand while inspecting every tooth of the ring
- Clean rust scale and packed debris from the tooth gaps and check the ring is fully seated and not lifted by corrosion
- On bearings with a magnetic encoder, check the seal for scoring and grease contamination and compare signal amplitude with the other side
- Confirm the tooth count matches the opposite wheel and the specification for the vehicle
- Check the wheel bearing for play and roughness
- Replace the tone ring or the complete hub assembly, then verify a clean, even signal on a road test