What does it mean?
C1204 is a Chassis (ABS, traction control, steering) fault code. It indicates: Wheel Speed Sensor Front-RH Range / Performance / Intermittent .
Symptoms
- ABS and stability control lamps that come on during a drive rather than immediately at start-up
- ABS or traction control cutting in briefly for no reason, often at low speed just before the car stops
- Front right wheel speed lags, spikes or drops out in live data while the other three agree
- Brake pedal pulsing unexpectedly on a dry, level road
- Fault clears after a restart and then returns after a certain speed or a particular corner
Likely causes
- Cracked or partly rusted tone ring producing uneven pulse spacing
- Air gap too large because of corrosion behind the sensor in the hub bore, or a sensor not pushed fully home
- Metal debris clinging to the sensor tip and distorting the signal
- Worn wheel bearing allowing hub movement, so the signal fades and returns with cornering load
- Intermittent break or high resistance inside the sensor lead that only shows up with vibration
- Significantly mismatched tyre size or pressure on that corner compared with the others
- Water in the connector adding resistance and rounding off the signal edges
How to fix it
- Record live wheel speeds from all four channels on a road test and look for the one that lags, spikes or drops out
- Check tyre sizes and pressures on all four corners before touching the sensor, since a mismatch alone can set this code
- Remove the sensor, clean the tip and the bore, and check for corrosion that would have increased the air gap
- Rotate the wheel by hand and inspect the tone ring around its full circumference for cracks, rust swelling and damaged teeth
- Check wheel bearing play and rotate the hub listening and feeling for roughness
- Inspect and wiggle test the sensor lead at every clip and flex point while watching live data
- Replace the sensor if its output is weak, and the hub or bearing assembly if the tone ring is damaged, then verify all four speeds track together