C0040: How to Diagnose & Fix — Right Front Wheel Speed Sensor Circuit
31 vehicles · 12 makes · $20-$1,500 repair
How to diagnose and fix C0040: most-reported vehicles
Ranked by owner reports. Each card gives the symptoms, how to confirm the cause, the fix, parts and sources for that vehicle.
Ford Focus · 2000–2007
1999-2007 Ford Focus (1st-generation Mk1 and Mk1.5) suffer from repeated rear wheel bearing failures, often within months of replacement. One Focus Fanatics owner reported the left rear wheel bearing failing 4 times in 7 months. Root cause is missing or degraded inboard spindle seals that allow brake dust and water into the bearing race, plus alignment drift (excessive negative camber or toe) accelerating wear. Ford acknowledged the seal design in owner communities but never issued a formal recall. Replacement requires the full hub assembly. The 2012-2018 Mk3 Focus has separate bearing issues with different root causes (not covered by this entry).
Common Symptoms
- Humming or growling noise from rear wheels that increases with speed
- Rumbling noise that changes pitch when turning (load shifts off bearing)
- Vibration felt through vehicle floor
- Uneven rear tire wear
- ABS warning light if bearing play affects wheel speed sensor
- Loose or wobbly feeling in rear end
- Grinding noise from rear at highway speeds
How to Fix
Replace the rear wheel bearing/hub assembly as a complete unit - the bearing is sealed and non-serviceable. RepairPal estimates $317-429 per side. When replacing, clean the knuckle bore thoroughly and apply anti-seize compound to prevent the new bearing from seizing in the housing (makes future replacement much easier). If the vehicle is in a salt-belt state, replace both rear bearings simultaneously - the other side will likely fail soon after.
Sources for this issue (1)
Chrysler 300 · 2011–2023
ABS control module suffers internal failures due to short circuits in main circuit board. Prevents proper ABS operation and stores fault codes. While regular braking functions, vehicle loses anti-lock capability, traction control, and stability control.
Common Symptoms
- ABS warning light constantly illuminated
- BAS warning light
- Traction control warning
- U0121 code (lost communication with ABS)
- No ABS function during hard braking
How to Fix
ABS module replacement or professional rebuild service. Check all wheel speed sensors and wiring before replacement. Many specialty shops offer rebuild for $300-500 with warranty. OEM module requires programming to VIN.
Sources for this issue (1)
GMC Sierra 1500 · 2014–2023
The electronic brake control module (EBCM) experiences failures causing ABS, traction control, and stability control systems to malfunction. Issues range from warning lights illuminating to complete system failures. The 2023 models have a specific recall for software that may fail to display a warning light when brake fluid loss occurs.
Common Symptoms
- ABS warning light illuminated
- Traction control and stability control warning lights
- Service Brake Assist message on dash
- ABS system activates unexpectedly or not at all
- Brake pedal feels different or spongy
- Multiple warning lights illuminate simultaneously
How to Fix
EBCM software reprogramming at dealer. EBCM replacement. Wheel speed sensor replacement if sensor-related. Check and repair wiring connections.
Sources for this issue (1)
Nissan 370Z · 2009–2014
Chevrolet Avalanche · 2002–2006
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C0040 code reference
General diagnostic-code context. The code alone does not confirm a cause for your vehicle; use the applicable issue card and its sources.
Frequently asked questions
What does C0040 mean?
C0040 stands for "Right Front Wheel Speed Sensor Circuit." This is a brake/ABS-system code. The right front wheel speed sensor measures how fast that wheel is rotating and feeds that data to the anti-lock brake, traction control, and stability control systems. C0040 means the ABS module found an electrical problem in the right front wheel speed sensor circuit — for example an open circuit, a short, or a signal that is missing or out of range. You'll normally see the ABS and traction/stability lights come on, and those systems may shut off temporarily while your regular brakes keep working.
What are the most common causes of C0040?
The most common causes of C0040 are: Failed right front wheel speed sensor, Damaged, corroded or unplugged sensor wiring/connector, Damaged or rust-clogged tone/reluctor ring, Excessive air gap between sensor and tone ring, Wheel bearing wear affecting an integrated sensor, Water intrusion or corrosion at the connector, Faulty ABS control module (less common). The specific cause varies by vehicle.
How much does it cost to fix C0040?
Repair costs for C0040 range from $20 to $1,500, depending on the vehicle and root cause.
Which vehicles are affected by C0040?
Au7o has documented C0040 across 31 vehicle models from 12 manufacturers: Chevrolet, Chrysler, Ford, GMC, Honda, Jeep, Lincoln, Nissan, Pontiac, RAM, Subaru, Toyota.
Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.