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DTC codes / C00xx · Brakes, steering and suspension / C0056

C0056Left Rear Wheel Speed Sensor Circuit Intermittent

The C0056 code indicates that the anti-lock brake system (ABS) control module has detected an intermittent fault in the left rear wheel speed sensor circuit. This means the signal from that sensor momentarily drops out or becomes erratic, but the fault is not present at the time of diagnosis, so the ABS warning light may be on or may have turned off.

SystemChassis
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyIntermediate
AreaBrakes, steering and suspension

Symptoms you may notice

  • ABS warning light illuminated on the dashboard, sometimes intermittently
  • Traction control or stability control warning light may also come on
  • Often no symptoms besides the warning light
  • Momentary wheel lockup or ABS activation during braking, especially at low speeds
  • Erratic speedometer readings if the sensor signal is used for vehicle speed
  • Intermittent operation of cruise control or other systems relying on wheel speed

Common causes, most likely first

  1. Damaged or chafed wiring in the left rear wheel speed sensor circuit
  2. Corroded or loose electrical connector at the sensor or harness
  3. Debris or metallic particles on the sensor tip or tone ring
  4. Faulty left rear wheel speed sensor
  5. Damaged or cracked tone ring (reluctor wheel) on the left rear hub
  6. Excessive wheel bearing play or hub runout affecting sensor signal
  7. Intermittent internal fault in the ABS control module

How to diagnose and fix it

  1. Inspect the left rear wheel speed sensor connector and harness for corrosion, looseness, or damage; clean and secure as needed
  2. Remove the sensor and check for metallic debris or damage on the sensor tip and tone ring; clean or replace if necessary
  3. Perform a wiggle test on the sensor wiring while monitoring live wheel speed data to reproduce the intermittent fault
  4. Measure the sensor resistance and compare to specification; replace the sensor if out of range
  5. Check the tone ring for cracks, missing teeth, or excessive runout; replace the hub or tone ring if faulty
  6. Verify the wheel bearing for excessive play and replace if needed
  7. If all external components test good, diagnose the ABS control module for internal faults

Intermittent faults demand a different approach

  • An intermittent wheel speed sensor code often sets because of a poor connection that only acts up under vibration or temperature changes, so a thorough wiggle test of the harness is more valuable than static resistance checks.
  • Debris or rust buildup on the sensor tip or tone ring can cause a dropout that mimics a failed sensor, so cleaning these components sometimes resolves the code without any parts replacement.
  • A worn wheel bearing or excessive hub runout can create an erratic signal that sets an intermittent code, and this is frequently overlooked when only the sensor and wiring are inspected.
  • The ABS module may set this code due to a momentary signal loss that occurs during specific driving conditions, such as hitting a bump or turning, so test-driving on varied road surfaces can help reproduce the fault.
  • Do not assume the sensor itself is defective; the code specifically indicates an intermittent circuit fault, which often lies in the wiring or connectors rather than the sensor.

Can I keep driving with C0056?

You can generally continue driving with this code, but be aware that the ABS may not function correctly during an emergency stop, so maintain extra following distance and avoid hard braking. Have the fault diagnosed soon to ensure full safety system operation.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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