Right Front Wheel Speed Circuit Malfunction (GM)
The C0040 code means the vehicle's onboard diagnostic system has detected: Right Front Wheel Speed Circuit Malfunction (GM). This is a serious severity code.
- Keep driving?
- Yes, but fix soon
- DIY difficulty
- moderate
- Estimated cost
- $100 - $600 (wheel-speed sensor or wiring most often; EBCM/pump work costs more)
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Common Symptoms
- ABS and/or traction control warning lights on
- ABS and stability assist may be disabled (base brakes still work)
- Possible false ABS activation at low speed with a failing wheel-speed sensor
Probable Causes (Ranked by Likelihood)
- Fault in the ABS/traction control component this code names (Right Front Wheel Speed Circuit Malfunction) High
- Damaged wiring or a corroded connector in that circuit - road-splash zones corrode connectors High
- Failed related sensor or actuator Moderate
- Control module fault Low
Common Fixes by Vehicle
What techs usually find when diagnosing C0040 on specific vehicles — tap your vehicle for the fix and the exact part:
2007-2018 Chevrolet Silverado/GMC Sierra easy DIY
Right front wheel speed sensor -- same failure mode as the left side (C0035). The sensor corrodes at the connector. Replace the sensor, clean the tone ring surface, and apply dielectric grease. If both front sensors set codes simultaneously, check the EBCM ground connection on the frame -- a bad ground will affect both channels.
Labor: 30-45 min2007-2017 Chevrolet Tahoe/Suburban/Yukon easy DIY
Check the sensor connector and wiring harness first. On the passenger side, the harness routes near the exhaust and can melt or become brittle. If the wiring is damaged, repair with heat-resistant wire and solder rather than butt connectors -- the vibration will shake butt connectors loose. Replace the sensor if the wiring is intact.
Labor: 30 min - 1 hour2008-2017 Chevrolet Equinox/GMC Terrain moderate DIY
Right front hub assembly replacement required -- the speed sensor is integrated into the hub. Same procedure as the left side. Jack up the vehicle, remove the brake caliper and rotor, disconnect the hub wiring, remove the 3 hub bolts (15mm), and pull the hub. Install the new hub, making sure the sensor connector is properly routed away from the brake rotor heat shield.
Labor: 1-2 hoursFrequently Asked Questions
What does C0040 mean?
C0040 is a chassis code used primarily by GM vehicles: Right Front Wheel Speed Circuit Malfunction. It concerns the ABS/traction control system.
Can I keep driving with C0040?
Base brakes keep working, but assume ABS and stability control are offline until repaired - allow longer stopping distances and drive gently, especially in rain or snow. Repair promptly.
Is C0040 the same on every make?
The decimal C0xxx range is dominated by GM's assignments (Chevrolet, GMC, Buick, Cadillac). Other makes may use this ID differently - if your vehicle is not a GM product, verify the meaning in your make's service information.
Mechanics Guide Step-by-step diagnosis, and what most sources get wrong
Step-by-Step Diagnostic Procedure
-
Read the code with a GM-capable scan tool and note the symptom byte/subcode if shown.
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View live data for the named circuit (e.g. all four wheel speeds while rolling for wheel-speed codes).
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Inspect the circuit's wiring and connectors - chassis harnesses live in the splash zone and corrode first.
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Follow the GM pinpoint test for C0040 before replacing components.
Common Misconceptions / Fact Check
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Commonly claimedMany guides say to ohm-test the wheel speed sensor (around 1000-2500 ohms) for C0040.
VerifiedThe 1,000-2,500 ohm figure applies to passive (magnetic) wheel-speed sensors. The vehicles that set C0040 use active Hall-effect sensors, which must not be resistance-tested -- applying an ohmmeter can damage a functioning sensor. Confirm reference voltage and observe the digital signal on a scope instead.
Sources 1
This page is built from documented references. Verify against your own service info before repair work.
- SAE J2012Diagnostic Trouble Code Definitions (defines the generic OBD-II code ranges)
C0040 on Diesel, EV & Equipment
The same code ID appears across other engines and platforms. The diagnostic flow varies by manufacturer — these are the platform-specific breakdowns:
Commonly Affected Vehicles
- Chevrolet, GMC, Buick, Cadillac (GM chassis code range)
Related Codes
See All Codes & Fixes for Your Vehicle
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