ABS wheel speed sensor · Chassis code
ABS wheel speed sensor codes
The anti-lock brake system has lost a trustworthy speed reading from one of the wheels, so it switches off ABS, and usually traction and stability control with it.
What this code means
Each wheel has a speed sensor that reads a toothed or magnetic ring turning with the hub. The ABS module compares all four wheels many times a second. If one wheel suddenly slows compared with the others during braking, ABS knows it's about to lock and releases pressure to that wheel.
When one sensor's signal disappears, goes out of range, or disagrees with the others, the module can't do that job safely, so it sets a code and turns ABS off. The code tells you which wheel: in the standard codes, C0031 is left front, C0034 right front, C0037 left rear and C003A right rear. The C0500–C0517 range adds detail such as circuit open, low, high or erratic for each wheel.
Chassis codes vary more by manufacturer than engine codes do. Many GM vehicles, for example, report wheel speed sensor faults as C0035, C0040, C0045 and C0050 for the four wheels instead. If your scanner shows a different number with “wheel speed sensor” in the description, the same advice applies.
Symptoms you may notice
- ABS warning light on, often with the traction control or stability light
- ABS doesn't activate on slippery roads (wheels can lock in a hard stop)
- Speedometer drops out or behaves erratically on some vehicles
- Pulsing brake pedal at low speed when it shouldn't (sensor reading falsely)
Common causes, most likely first
- Failed wheel speed sensorThe most common cause. Sensors live in a harsh spot near the brakes and get heat, water and road salt.
- Damaged sensor wire or connectorThe wire flexes with the suspension and can chafe, break or corrode, especially near the connector.
- Dirty or damaged tone ringRust buildup or a cracked ring on the axle or hub gives the sensor a bad signal. Common on older vehicles in salt-belt states.
- Worn wheel bearing / hubOn many cars the sensor or its magnetic ring is built into the hub. Excess bearing play also changes the gap the sensor reads across.
- Recent brake or suspension workA sensor that was pulled, stretched, or left unplugged during a brake job.
What to check first
- Find out which wheel the code points to. A basic code reader may not read ABS codes, so you may need a scan tool with ABS access or a parts store or shop that has one.
- Look at that wheel's sensor wire from the sensor to the body connector. Check for breaks, rubbed-through insulation and corroded connectors.
- Ask whether brakes, hubs or axles were recently serviced on that corner.
- A shop can watch live wheel speeds while driving; the bad wheel usually reads zero or drops out.
- Check the wheel bearing for play or noise (a humming that changes with speed), since a worn hub is a common root cause.
Typical repairs and rough cost
| Repair | Typical cost | Notes |
|---|---|---|
| Wheel speed sensor (one wheel) | $100–$300 | Rear sensors are sometimes harder to remove because of corrosion. |
| Sensor wiring repair | $100–$250 | |
| Hub/bearing assembly with built-in sensor | $250–$600 | Per wheel; fixes a noisy bearing at the same time. |
| Tone ring cleaning or replacement | $50–$400 | Cleaning is often enough; ring replacement can mean an axle or hub. |
Rough US shop prices for parts and labor. Your cost depends on the vehicle, the parts brand and local labor rates.
Official code definitions
| Code | Applies to | Definition |
|---|---|---|
| C0031 | Generic | Left Front Wheel Speed Sensor |
| C0034 | Generic | Right Front Wheel Speed Sensor |
| C0037 | Generic | Left Rear Wheel Speed Sensor |
| C003A | Generic | Right Rear Wheel Speed Sensor |
| C0500 | Generic | Left Front Wheel Speed Sensor A Circuit/Open |
| C0506 | Generic | Right Front Wheel Speed Sensor A Circuit/Open |
| C050C | Generic | Left Rear Wheel Speed Sensor A Circuit/Open |
| C0512 | Generic | Right Rear Wheel Speed Sensor A Circuit/Open |
| C0040 | Audi | A faulty wheel speed sensor, A problem with the wheel speed sensor circuit, Reluctor issues, A problem with the ABS module |
“Generic” codes mean the same thing on every make. Manufacturer entries are that brand’s own description. Look up any other code in the code library.
Common questions
Is it safe to drive with the ABS light on?
Your regular brakes still work, so the car will stop. What you lose is anti-lock, traction and stability control, which matter most in emergency stops and on wet or icy roads. Get it fixed soon and drive with extra margin until then.
Why won't my code reader show the ABS code?
Many inexpensive OBD-II readers only read engine codes. ABS codes need a scanner that can talk to the brake module. Many parts stores and every shop have one.
Can one bad sensor turn off traction control too?
Yes. Traction and stability control rely on the same wheel speed signals, so they usually shut off along with ABS.
Related codes
This guide explains what the code usually means and how it’s typically diagnosed. Every car is different, and a code points to a system, not always a specific part. For anything affecting brakes, steering or a car that feels unsafe, have a qualified mechanic confirm before you rely on it.