C0040 on Subaru: How to Diagnose & Fix
Right Front Wheel Speed Sensor Circuit
1 Subaru model · 1 documented issue · $250-$600 repair
C0040 on Subaru by model: symptoms, diagnosis and fix
Forester wheel bearings (both front and rear hub assemblies) fail prematurely, often well before 100,000 miles. The most consistent symptom is a low-pitched grinding, humming or 'airplane' droning noise from the affected corner that grows louder with speed; rear bearing wear is often felt as a vibration under the seats. The noise typically changes pitch or volume during a left/right lane-change maneuver (which distinguishes it from differential whine). Subaru acknowledged a contributing root cause: unevenness/distortion of the bearing backing plate surface affects hub/bearing concentricity after the axle nut is torqued, allowing a 'howling' bearing to develop over time. Water/dirt contamination from failed seals and improper axle-nut torque accelerate the wear. Subaru issued a service bulletin acknowledging the rear bearing/backing-plate concern.
Common Symptoms
- Grinding or humming/droning noise from a wheel that gets louder with speed
- Noise changes during left/right lane-change maneuvers
- Vibration felt under the seats (rear bearing)
- Knocking or clunking when cornering
- Uneven/inner-edge tire wear
- Play when rocking the wheel by hand
How to Fix
Diagnose by lifting the wheel and checking for play/roughness, and by listening for a noise that changes during gentle S-turns at 30-65 mph. The fix is replacement of the complete wheel hub/bearing assembly (sold as a unit). On 2014-2018 Foresters the front complete hub unit is OEM 28473FL040 (supersedes 28473FJ000/28473FJ020); reuse a new self-locking axle nut and torque to spec. Have an alignment checked, as poor alignment and unbalanced tires accelerate bearing failure. Replacing in pairs is common practice.
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
- Genuine Subaru 28373FG000 Front Hub and Bearing Assembly
front hub only after the front bearing is localized and confirmed failed Fitment/availability: 2009-2013 Forester front, plus the early-2014 production branch through the catalog split; confirm VIN and side Fitment/availability: Add to C…
- Genuine Subaru 28473FG000 Rear Hub Unit, Superseded by 28473FL021
rear hub only after the rear bearing is localized and confirmed failed Fitment/availability: 2009-2013 Forester rear branch; confirm VIN and current 28473FL021 supersession Fitment/availability: ships in 1-2 business days with Add to Car…
- Genuine Subaru 28373SC000 Front Hub Unit, Superseded by 28373FL011
front hub only after the front bearing is localized and confirmed failed Fitment/availability: 2014-2018 Forester front branch after the early-2014 production split; confirm VIN and current 28373FL011 Fitment/availability: Add to Cart li…
- Genuine Subaru 28473FL040 Rear Hub Unit, Superseded by 28473FL041
rear hub used with the applicable updated backing plate under TSB 05-70-19R Fitment/availability: 2014-2018 Forester rear position only; confirm VIN and current 28473FL041 supersession Fitment/availability: Add to Cart live with current …
- Genuine Subaru 26704FJ012 Left Rear Backing Plate
left-side companion required by TSB 05-70-19R when repairing that defined rear howling condition Fitment/availability: 2014-2018 Forester left/driver rear, updated backing-plate branch; confirm VIN Fitment/availability: Add to Cart live …
- Genuine Subaru 26704FJ002 Right Rear Backing Plate
right-side companion required by TSB 05-70-19R when repairing that defined rear howling condition Fitment/availability: 2014-2018 Forester right/passenger rear, updated backing-plate branch; confirm VIN Fitment/availability: ships in 1-3…
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Sources for this issue (3)
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 Subaru?
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 Subaru it is documented across 1 model: Forester.
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 Subaru?
Published repair estimates on Subaru range from $250 to $600 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.