C0040 on Ford: How to Diagnose & Fix
Right Front Wheel Speed Sensor Circuit
2 Ford models · 2 documented issues · 1 critical · $120-$650 repair
C0040 on Ford by model: symptoms, diagnosis and fix
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)
Transit Connect owners report intermittent ABS and traction control warnings caused by wheel speed sensor signal dropouts, often due to sensor contamination, corrosion at connectors, or damaged wiring near the hubs. The issue can be intermittent and may also disable stability control functions until repaired. This pattern appears in NHTSA complaints and owner reports describing ABS/AdvanceTrac warnings and sensor replacement.
Common Symptoms
- ABS warning light illuminated
- Traction control/AdvanceTrac warning
- ABS activates unexpectedly at low speed (sometimes)
- Speedometer fluctuation (rare)
- Stored wheel speed sensor DTCs
How to Fix
Scan ABS module for wheel speed sensor DTCs and view live wheel speed data to identify the affected corner. Clean/inspect tone rings (if applicable), repair wiring/connectors, or replace the wheel speed sensor; clear codes and verify on a road test.
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
- ABS Wheel Speed SensorCross-refSS20881
Fitment confirmed against the ShowMeTheParts catalog for this vehicle's year and engine.
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Sources for this issue (1)
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 on a Ford?
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. On Ford it is documented across 2 models: Focus, Transit Connect.
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 on a Ford?
Published repair estimates on Ford range from $120 to $650 depending on the model and root cause. If an issue mentions a recall or campaign, check your VIN with the manufacturer or NHTSA and confirm eligibility and coverage with a dealer.
Looking for C0040 on a different make?
View C0040 across all makes →Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.