ABS and brakes

C0038 — Right Rear Wheel Speed Sensor Circuit Low Input

Severity: medium Drive with care, to a shop

What C0038 means

The ABS control module constantly reads each wheel speed sensor and compares the signals. C0038 means the voltage in the right rear sensor circuit is lower than expected, so the signal is missing or too weak. Without reliable wheel speed data, the module typically disables ABS and often traction and stability control too.

Symptoms

  • ABS warning light on
  • Traction or stability control light may come on
  • ABS and traction control not working
  • Check Engine light on some AWD models
  • Erratic speedometer on vehicles that use this signal for it

Possible causes

  1. Failed right rear wheel speed sensor
  2. Open circuit or short to ground in the sensor wiring
  3. Corroded or damaged connector
  4. Worn rear wheel bearing changing the sensor gap or causing tone ring runout
  5. Dirty or damaged sensor tip or tone ring, or metal debris on the magnet
  6. Faulty ABS module (uncommon)

How to diagnose

  1. Scan the ABS module and watch live data: right rear wheel speed should match the other wheels while driving
  2. Inspect the sensor wiring near the right rear wheel for chafing, breaks, or past repairs
  3. Check the connector for moisture, corrosion, and a secure fit
  4. Remove the sensor and inspect its tip and the tone ring for dirt, debris, cracks, or missing teeth
  5. Check the wheel bearing for play and confirm the sensor is seated with the correct air gap
  6. Measure sensor resistance and signal or supply voltage per the factory procedure, and test the wiring for opens and shorts
  7. If the sensor and wiring are good, check the ABS module connector and power supply

Common fixes

  • Replace the right rear wheel speed sensor
  • Repair or replace damaged wiring or the connector
  • Clean the sensor and tone ring and restore the proper gap
  • Replace the wheel bearing or tone ring
  • Repair or replace the ABS module only after ruling out everything else

Questions and answers

Can I drive with code C0038?

Yes, but carefully. The base brakes still work, but ABS and stability control are most likely disabled, so wheels are more likely to lock on wet or slippery roads.

What most often causes C0038?

Most often it is a bad right rear wheel speed sensor or damaged wiring near it. Also check the wheel bearing and the condition of the tone ring.

Why would C0038 turn on the Check Engine light?

On some AWD vehicles, wheel speed data is also used by the engine and drivetrain controls. Losing that signal can trigger the engine light as well.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.