ABS and brakes

C0037 — Left Rear Wheel Speed Sensor Circuit Low Input

Severity: medium Drive with care, to a shop

What C0037 means

The ABS control module detected that the signal or voltage in the left rear wheel speed sensor circuit is lower than expected. The sensor normally produces pulses as the tone ring or magnetic encoder on the hub turns, and the module compares those pulses across all wheels. Without a reliable signal from this wheel, ABS and stability control cannot work properly, so the module disables them.

Symptoms

  • ABS warning light on
  • Stability or traction control light on
  • ABS does not activate in hard braking
  • Speedometer problems on some vehicles
  • Fault comes and goes over bumps

Possible causes

  1. Failed left rear wheel speed sensor
  2. Damaged, chafed or broken sensor wiring
  3. Corroded or dirty connector causing poor contact
  4. Short to ground in the sensor circuit
  5. Dirt, metal debris or rust on the tone ring or sensor
  6. Damaged tone ring or magnetic encoder in the hub
  7. ABS module fault (uncommon)

How to diagnose

  1. Scan the ABS module and compare live wheel speed data for all four wheels
  2. Inspect the sensor, harness and connector at the left rear wheel for damage, rubbing or corrosion
  3. Remove the sensor and check for dirt, metal debris or damage
  4. Inspect the tone ring or encoder for cracks, rust or missing teeth
  5. Check sensor mounting and air gap
  6. Measure sensor resistance against specification (for inductive sensors)
  7. Test the wiring for opens and shorts to ground, flexing the harness while testing
  8. Clear the code and road test to see if it returns

Common fixes

  • Clean the sensor and tone ring
  • Replace the left rear wheel speed sensor
  • Repair or replace the damaged wiring harness
  • Clean or replace the connector
  • Replace the wheel bearing with encoder or the tone ring

Questions and answers

Can I drive with a C0037 code?

Yes, carefully. Normal brakes should still work, but ABS and stability control are off. Leave extra stopping distance on wet or slippery roads and fix it soon.

What most often causes C0037?

Usually the sensor itself or its wiring near the wheel, where it is exposed to dirt, water and damage. A dirty tone ring can also cause it.

Can I just clear the C0037 code?

Clearing it may turn the light off briefly. If the cause remains, the code will return and ABS and stability control will shut off again.

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.