C0038 – Left Rear Wheel Speed Sensor Supply (OBD2)
C0038 means "Left Rear Wheel Speed Sensor Supply". Each wheel has a speed sensor that reads a toothed or magnetic tone ring; these codes mean the ABS module has detected a missing, implausible or electrically faulty wheel speed signal.
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C0038 quick summary
| Fault code | C0038 |
|---|---|
| Meaning | Left Rear Wheel Speed Sensor Supply |
| System | Chassis |
| Vehicles | Generic OBD2 |
| Severity | Medium |
| Can I drive? | Yes, carefully. ABS, traction and stability control are usually disabled, and the speedometer or gearbox may be affected. Keep more distance and avoid hard braking on slippery roads. |
| Repair cost | €20 – €400 |
How wheel speed sensors work
Modern cars use active (Hall or magnetoresistive) wheel speed sensors that read a magnetic encoder ring in the wheel bearing or a toothed tone ring on the drive shaft or hub. The ABS module supplies the sensor and receives a square-wave signal whose frequency rises with wheel speed. Older cars use passive inductive sensors that generate their own AC voltage.
The ABS module compares all four wheels. Codes report an open or shorted circuit, a signal out of range, an erratic or missing signal, a mismatch with the other wheels (correlation), a damaged tone wheel or a wrong sensor type fitted. Because the vehicle speed for the engine, gearbox, speedometer and cruise control often comes from these sensors, one faulty wheel can affect many systems.
Typical causes are rust lifting the sensor away from the ring, metal debris on the sensor tip, a cracked or corroded tone ring, a damaged magnetic seal in a wheel bearing (often after a bearing was fitted the wrong way round), broken wiring near the suspension and corroded connectors.
The code refers to the left rear wheel. Left and right are always seen from the driver's seat looking forward – on a left-hand-drive car the left side is the driver's side.
C0038 is a chassis code in the standard (SAE) numbering. Some manufacturers – for example GM, Opel and Ford on certain models – use their own meanings for some C codes, so always check the text your scan tool shows for your vehicle.
Symptoms of C0038
- ABS, ESP and traction control lights on
- Light comes on only above a certain speed or on rough roads
- Speedometer or cruise control not working (some cars)
- ABS activates at low speed when braking gently
- Harsh shifting or limp mode on automatic gearboxes
Most common causes of C0038 (most likely first)
Mechanic's Pro Tip
If a new sensor does not fix the code, look at the tone ring and the wheel bearing. A bearing fitted with the magnetic encoder facing away from the sensor, or a rusty tone ring on the drive shaft, produces exactly the same code as a dead sensor.
1.Failed wheel speed sensor
Most likelyInternal failure, often after heat or water ingress.
2.Dirt or metal debris on the sensor tip, or rust lifting the sensor
Increases the air gap so the signal becomes weak or erratic.
3.Damaged, cracked or corroded tone ring
Tone rings on drive shafts rust and crack; magnetic encoders in bearings get damaged.
4.Wheel bearing fitted the wrong way round or worn
The magnetic encoder side must face the sensor; excessive play changes the air gap.
5.Broken wire or corroded connector near the wheel
Wiring flexes with the suspension and is exposed to water and salt.
Step-by-step diagnostic guide
- 1
Read codes and compare wheel speeds
Read the ABS module and watch all four wheel speeds in live data while driving slowly in a straight line. The faulty wheel shows zero, drops out or differs from the others.
- 2
Inspect sensor, wiring and connector
Check the sensor and its cable along the suspension for damage, and the connector for corrosion. Swap the front sensors left/right if possible to see if the fault moves.
- 3
Measure the sensor
Check supply and signal on active sensors; resistance and AC output on passive sensors.
Multimeter: Active sensors: supply from the module usually about 8–12 V (two-wire current signal around 7/14 mA). Passive sensors: often about 0.8–2.5 kΩ and an AC voltage rising with wheel speed.
- 4
Check the tone ring and bearing
Remove the sensor, clean the bore and check the tone ring or magnetic encoder for cracks, missing teeth, rust and correct bearing orientation.
- 5
Repair and test drive
Replace the sensor, ring or bearing as needed, clean and lightly grease the sensor bore, clear the codes and confirm all four wheel speeds match on a test drive.
Frequently asked questions
Can I keep driving with C0038?
Yes, carefully. ABS, traction and stability control are usually disabled, and the speedometer or gearbox may be affected. Keep more distance and avoid hard braking on slippery roads.
How much does it cost to fix C0038?
Typical repair costs are 20 € – 400 €, depending on the cause and the vehicle. The most common fixes are: failed wheel speed sensor; dirt or metal debris on the sensor tip, or rust lifting the sensor; damaged, cracked or corroded tone ring. Always confirm the cause with the tests above before buying parts.
Which wheel is the faulty one?
The code names the position. Left and right are seen from the driver's seat looking forward. Confirm it by comparing the four wheel speeds in live data before buying parts.
Can a bad wheel speed sensor affect the gearbox?
Yes. On many cars the vehicle speed signal for the engine, gearbox and speedometer comes from the ABS sensors, so one faulty sensor can cause harsh shifts or limp mode.
What is the difference between C0038 and similar codes?
C0038 belongs to a group of codes for the same component that differ in the type or location of the fault: C0035 – Right Front Wheel Speed Sensor Supply; C0036 – Left Rear Tone Wheel; C0037 – Left Rear Wheel Speed Sensor; C0039 – Right Rear Tone Wheel; C003A – Right Rear Wheel Speed Sensor; C003B – Right Rear Wheel Speed Sensor Supply. The tests on this page apply to the whole group; the type of fault tells you where to start.
Related fault codes
This guide is for information only. Working on vehicles can be dangerous — if you are unsure, have the car checked by a qualified mechanic. Values can differ between model years; always check the manufacturer's repair information.