Is it safe to drive with C0040?

Your normal brakes still work, so you can stop the car. But ABS, traction control, and stability control are disabled, which matters most in hard stops, rain, snow, or on gravel where those systems help you keep control. It's safe to drive gently to get it repaired, but you shouldn't rely on anti-lock or traction assistance until the sensor is fixed.

What's the most likely cause of C0040?

A failed right front wheel speed sensor or damage to its wiring and connector. That sensor sits down by the wheel and is exposed to water, road salt, and debris, so corrosion and chafed wiring are common. A rusted or debris-packed tone ring can also mimic a bad sensor. Inspecting the sensor, connector, and tone ring usually points to the fix before any part is replaced.

C0040 and C0035 are both set — what does that mean?

C0040 is the right front wheel speed sensor and C0035 is the left front. Two front sensors failing at exactly the same time is uncommon, so when both codes appear together it's smarter to look for a shared cause — a common connector or ground, a wiring harness both circuits pass through, or an ABS module fault — before replacing two sensors.

Why did my traction and stability lights come on with C0040?

Traction control and stability control both rely on the same wheel speed sensors as ABS. When the module loses a trustworthy signal from one wheel, it can no longer run any of those functions safely, so it disables all of them at once and lights the corresponding warnings. Fixing the wheel speed sensor fault typically restores all three systems together.

OBD-II trouble code

C0040: Right Front Wheel Speed Sensor Circuit

The ABS module detected a fault in the right front wheel speed sensor or its circuit. The ABS and traction/stability warning lights typically come on and those systems are disabled, but normal (base) braking still works.

Quick facts

System: Chassis
Category: ABS / Wheel Speed
Severity: Medium severity
Drivable: Usually safe to drive short-term
Repair cost range: $100 – $400
DIY difficulty: Intermediate DIY

What does C0040 mean?

Each wheel has a speed sensor that reports how fast that wheel is turning to the anti-lock brake system (ABS) module. The module compares all four wheel speeds to detect a wheel about to lock under braking (ABS), a wheel that is spinning (traction control), or a vehicle that is sliding (stability control). C0040 sets when the module sees a fault in the right front wheel speed sensor circuit — the signal is missing, out of range, erratic, or electrically shorted or open — so it can no longer trust that wheel's speed reading.

Because the safety systems need a reliable speed signal from every wheel, losing one input causes the module to disable ABS, traction control, and stability control and turn on the associated dash warning lights. Your ordinary hydraulic brakes are not affected — the car stops normally — but the anti-lock and traction/stability functions that help in a hard stop or on slippery roads are switched off until the fault is repaired. C0040 is the mirror-image code to C0035 (left front); when the two set together, suspect a shared cause such as a common connector, ground, or the ABS module rather than two sensors failing at once.

The most common causes are a failed wheel speed sensor and, very often, damage at the sensor's exposed location: the right front sensor and its wiring sit down by the wheel and are exposed to road spray, salt, and debris, so corroded or broken connectors and chafed wiring are frequent culprits. A damaged or contaminated tone ring (the toothed reluctor the sensor reads) can also produce an erratic signal that mimics a bad sensor. Note that C0040 is the SAE-generic designation for the right front wheel speed sensor circuit; some manufacturers — General Motors in particular — assign wheel-speed faults to different C-code numbers or use C0040 with a sub-code, so always confirm the exact definition against service data for your specific vehicle before replacing parts.

Common causes

Failed right front wheel speed sensor
Corroded, broken, or loose connector at the sensor
Chafed, cut, or open wiring in the sensor circuit (road/salt exposure)
Damaged, cracked, or contaminated tone/reluctor ring
Excessive air gap from a loose sensor or hub/bearing play
ABS module fault (less common)

Symptoms

ABS warning light on
Traction control and stability control (ESC) warning lights on
ABS, traction, and stability features disabled
Normal (base) braking still works
Possible speedometer or cruise-control issues on some vehicles

Diagnostic steps

1.Scan the ABS module and record all C-codes and any sub-codes to confirm which wheel and what type of fault (low/open, erratic).
2.Inspect the right front wheel speed sensor, its connector, and wiring for corrosion, damage, or a loose connection.
3.Check the tone/reluctor ring for cracks, missing teeth, rust, or debris packed into the teeth.
4.Measure the sensor's resistance or output and compare wheel-speed live data across all four wheels while turning the wheel.
5.Verify the sensor air gap and that the sensor is seated properly with no hub-bearing play.
6.Repair or replace the sensor or wiring, clear the codes, and road-test to confirm all four wheel-speed signals track correctly.

Repair cost

$100 – $400

A wheel speed sensor is a common, moderate-cost repair: parts often run $30-$150 with about an hour of labor, so many C0040 repairs land around $100-$300. Wiring or connector repairs vary. On vehicles where the sensor is integrated into the wheel hub/bearing assembly, replacing the hub raises the cost. The sensor and its wiring are the most likely fix and should be checked first.

Estimate your repair

Run the numbers for your vehicle

Open the Repair Cost Estimator with wheel speed sensor replacement preselected. Adjust labor rate and vehicle category to fit your situation.

Estimate your repair cost

DIY vs shop

This is an intermediate DIY job. It usually involves diagnostic steps, specialty parts, and some careful work in tight spaces. If you have the tools and a service manual or trustworthy video for your specific vehicle, it is achievable in a weekend. Otherwise, a competent independent shop will be faster.

Related codes

C0035 C0045