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DTC codes / C00xx · Brakes, steering and suspension / C0066

C0066Right Rear Wheel Speed Sensor Circuit Intermittent

C0066 means the antilock braking system (ABS) control module has detected an intermittent signal from the right rear wheel speed sensor circuit. The computer sees the signal drop out or become erratic for brief moments, often too quickly to store a permanent fault, so it flags the circuit as unreliable rather than completely dead.

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

Symptoms you may notice

  • ABS warning light illuminated on the dashboard, often coming and going
  • Traction control or stability control warning light also on in many vehicles
  • ABS may temporarily disable, returning normal braking but without antilock assistance
  • Intermittent wheel speed dropout can cause a brief pulsation or grab in the brake pedal at low speeds
  • Speedometer needle may twitch or fluctuate if the sensor signal is used for vehicle speed
  • Often no symptoms besides the warning light, especially if the fault is very brief

Common causes, most likely first

  1. Damaged or chafed wiring harness near the right rear wheel, often from road debris or suspension movement
  2. Corroded or loose electrical connector at the right rear wheel speed sensor
  3. Debris or metallic particles stuck to the sensor tip or tone ring, disrupting the magnetic signal
  4. Worn or damaged tone ring (reluctor ring) on the right rear hub or axle
  5. Failing wheel speed sensor that works intermittently when hot or over bumps
  6. Excessive wheel bearing play or hub runout causing an erratic sensor gap
  7. Water intrusion into the sensor connector or wiring splice

How to diagnose and fix it

  1. Inspect the right rear wheel speed sensor wiring and connector for chafing, corrosion, or loose pins, and repair as needed
  2. Remove the sensor and clean the mounting surface and tone ring of any metallic debris or rust
  3. Check the tone ring for cracks, missing teeth, or excessive runout, and replace the hub or axle if damaged
  4. Measure the sensor air gap and compare to specification, adjusting or replacing components if out of range
  5. Perform a wiggle test on the harness while watching live wheel speed data to catch intermittent opens
  6. Replace the right rear wheel speed sensor if wiring and tone ring are good but the signal still drops out
  7. Clear the code and verify the repair by test-driving while monitoring wheel speed PIDs for all four wheels

Intermittent faults hide in plain sight

  • A wheel speed sensor can test perfectly with a multimeter and still be intermittent when vibration or heat changes the internal connection, so live data graphing during a road test is essential.
  • The ABS module often shares wheel speed signals with the transmission, stability control, and speedometer, so a right rear sensor fault can cause unrelated symptoms like harsh shifting or a fluctuating speedometer.
  • Metallic debris from a worn brake rotor or hub can stick to the sensor magnet and cause dropouts that mimic a failing sensor, so cleaning the tip often cures the code without parts.
  • Aftermarket brake pads or rotors with incorrect tone ring dimensions can create an intermittent signal that only appears at certain speeds, so verify part compatibility if the code appeared after brake work.
  • The code may set from a single brief dropout during a pothole impact, and if the wiring and sensor pass all tests, the fault may never return; clearing and monitoring is a valid first step.

Can I keep driving with C0066?

You can usually drive with C0066 because normal braking remains, but the ABS and stability control may be disabled, so avoid hard braking or slippery conditions until the fault is repaired. If the warning light is accompanied by a soft or pulsating brake pedal, have the vehicle inspected before driving further.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

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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