C0040 – Right Front Wheel Speed Sensor Circuit

What does C0040 mean?

The right front wheel speed sensor circuit has a malfunction. This sensor reports individual wheel speed to the ABS module, which uses it to detect lockup during braking and to support traction and stability control.

What causes C0040?

Listed from most to least common:

1. 1Damaged wiring at the wheel from constant suspension movement
2. 2Failed wheel speed sensor
3. 3Metal debris on the sensor tip
4. 4Damaged or rusted tone/reluctor ring
5. 5Corroded connector
6. 6Excessive wheel bearing play changing the sensor air gap

Code breakdown

Common symptoms

• ABS warning light on
• Traction and stability control lights on and systems disabled
• Possible speedometer irregularities on some vehicles
• Normal braking retained

How to diagnose

1. 1Inspect the sensor harness where it flexes near the wheel — the most common failure point.
2. 2Remove the sensor and check the tip for metal filings, which is a frequent and free fix.
3. 3Inspect the tone ring for cracked, rusted, or missing teeth.
4. 4Compare all four wheel speed readings in live data while driving slowly.
5. 5Measure sensor resistance against specification.
6. 6Check wheel bearing play.

ABS, traction control, and stability control are typically disabled. Normal braking still works, but anti-lock function may not — allow extra following distance in wet or icy conditions.

Common fixes and estimated costs

Costs are rough US estimates including parts and labor. Actual pricing varies significantly by vehicle, region, and shop rates.

Good to know

On many modern vehicles the tone ring is built into the wheel bearing hub, so a damaged ring requires replacing the entire hub assembly. Check for simple debris first before assuming the worst.

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