C0040 C0xxx · Chassis (C) High severity
Right Front Wheel Speed Sensor Circuit
Right front wheel speed signal lost or implausible. ABS, traction and stability functions are disabled.
Severity guidance: High — stop driving and diagnose now; risk of further damage
Symptoms you will notice
- ABS and ESP lamps on
- No ABS intervention
- Possible speedometer fault
Common causes
Ordered from most to least likely — start at the top.
- 1 Failed sensor
- 2 Damaged tone ring
- 3 Wiring damage near the strut
- 4 Corroded connector
How to diagnose it
Cheapest and least invasive first — most of these codes are not a parts problem.
- ✓ Read all four wheel speeds and find the outlier.
- ✓ Inspect the connector and the first 30 cm of wiring — this is where breaks hide.
- ✓ Check the tone ring through the sensor bore.
- ✓ Swap-test across left and right if the fault is intermittent.
Repair options
- Replace the sensor
- Repair the wiring
- Replace the hub with a damaged tone ring
C0040 — frequently asked questions
Can rust cause it? +
Yes. A rusting tone ring lifts and changes the air gap, and debris on a magnetic ring corrupts the signal.
Do I need to code a new sensor? +
Usually not for ABS sensors, but some manufacturers require a steering-angle or TPMS relearn afterwards.
Confirm the diagnosis before you buy parts
Send us the code, freeze-frame data and the vehicle — our engineers will tell you what to test first.