C0055 Code: Rear Wheel Speed Sensor Circuit (Single Rear Sensor)
The ABS module lost the combined rear-axle speed signal used on many GM trucks, vans and SUVs.
Unverified: this manufacturer-specific definition comes from a single source or varies by model. Confirm it with a brand-specific scan tool.
Safety first · Consult a professional
- Braking system affected: ABS may be disabled. Drive carefully and have it checked promptly.
At a glance
Severity: Moderate
- Meaning
- Rear Wheel Speed Sensor Circuit (Single Rear Sensor)
- System
- Brakes, ABS & Chassis · Chassis
- Safe to drive?
- With caution
- Typical repair cost
- $20–$300
- DIY difficulty
- Moderate
In GM numbering, C0055 is the rear wheel speed sensor circuit on vehicles that measure both rear wheels with one sensor instead of two. That sensor sits either in the rear differential housing, reading the ring gear or an exciter ring on the carrier, or in the transmission or transfer case output, where it may also feed the speedometer and shift logic. It's typical of rear-wheel ABS and three-channel systems on pickups, full-size vans and older SUVs. The newer SAE list uses C0055 for a steering wheel position sensor signal, so on other makes the meaning can be completely different; check your scan tool's description.
Can I keep driving? Brakes work, but rear ABS is off, so an empty pickup bed can let the rear wheels lock easily. If the speedometer or shifting is affected too, drive gently and don't rely on cruise control.
How to read C0055
- C Chassis
- 0 Generic (SAE)
- 0 Brakes, ABS & Chassis
- 55 Specific fault
Symptoms
- ABS light on, often with a dead or jumpy speedometer
- Harsh, late or early shifts on trucks where the same signal feeds the transmission
- Cruise control won't engage
- Rear wheels lock easily when braking with an empty bed
- Gear oil wetness around the sensor on the differential
- Engine code P0500 stored at the same time
Possible causes
Ranked by how often each cause is behind this code (editorial estimate).
- Sensor tip coated with metal particles from the differential or transmission
- Harness chafed where it crosses the axle, frame rail or transmission bellhousing
- Failed rear speed sensor
- Gear oil wicking past the sensor O-ring into the connector
- Damaged exciter ring, or wrong tire size/axle ratio programming making the signal implausible
- ABS module or speed-signal buffer fault
Diagnosis step by step
Confirm the definition and check other modules
Make sure your scan tool lists C0055 as the rear wheel speed sensor. Also read the engine and transmission computers; a matching P0500 or output-speed code confirms the shared sensor or its wiring rather than the ABS module.
Tools: OBD-II scanner
Find where your sensor lives
Look on top or at the front of the rear differential housing near the ring gear, and on the transmission tailshaft or transfer case. The service information for your vehicle tells you which one feeds the ABS.
Tools: Flashlight
Pull and clean the sensor
Remove the hold-down bolt and pull the sensor out. A furry coat of metal on the magnetic tip is normal wear debris but it weakens the signal; wipe it off, inspect the O-ring and check the gear oil level before reinstalling.
Tools: Screwdriver, Gloves
Measure resistance and output
These rear sensors are usually passive. Typical readings are roughly 1-2.5 kOhm between the two pins; with the rear raised and the transmission in neutral, turning one wheel by hand should produce a small AC voltage that rises as you spin faster.
Tools: Multimeter
Inspect the harness route
Follow the lead from the axle up to the frame and forward. Look for rubbing on the axle tube, stretched wiring at full suspension droop and melted insulation near the exhaust.
Tools: Flashlight
Check calibration after tire or gear changes
If larger tires or a different axle ratio were fitted, the module may expect a different pulse count. Reprogramming the tire size and axle ratio with a capable scan tool can be part of the fix.
Tools: OBD-II scanner
Where the parts are
- 1Battery
- 2Alternator
- 3Engine computer (ECM)
- 4CAN bus
- 5Transmission
- 6Wheel speed sensor
- 7High-voltage battery
Repair options & costs
| Repair | DIY? | Estimated cost |
|---|---|---|
| Clean sensor tip, replace O-ring, top up gear oil | Yes | $20–$120 |
| Replace rear speed sensor | Yes | $70–$250 |
| Repair chafed harness | No | $100–$300 |
| Reprogram tire size/axle ratio | No | $80–$180 |
Rough US estimates for parts and labor; shop rates vary by region. Not a quote.
Notes by brand
Chevrolet
On Chevrolet pickups, full-size vans and SUVs that use a single rear speed sensor, C0055 frequently shows up alongside a dead speedometer and erratic shifting, because the same signal is shared with the engine and transmission computers.
Emissions / smog test impact
Depends
C0055 by itself won't fail an OBD emissions test, but if P0500 is also stored the check engine light can. States with a safety inspection may reject a vehicle with the ABS light on.
Frequently asked questions
Why is there only one rear sensor on my truck?
Many pickups and vans use rear-wheel ABS or a three-channel system that controls both rear wheels together. One sensor on the differential or transmission output tells the module the average rear axle speed.
Can C0055 affect shifting and the speedometer?
Yes, on vehicles where the rear speed signal is shared. When the sensor fails, the speedometer may drop to zero and the transmission may shift at the wrong time along with the ABS light.
Is metal on the sensor tip a sign of a bad differential?
A light coating of fine particles is normal wear. Large chunks or chips point to gear or bearing damage and deserve a closer look at the differential.
My scanner says C0055 is a steering sensor. What gives?
The newer SAE list assigns C0055 to steering wheel position sensor signal D. That meaning applies on some non-GM vehicles, so follow the description your scan tool shows.
Sources
- SAE J2012 – Diagnostic Trouble Code Definitions
- Manufacturer public service information (cross-checked)
- Methodology: How We Build Code Pages · Data Sources We Use · Editorial Policy