01 P0071 Code: Ambient Air Temperature Sensor Range or Perform… • 02 Toyota Noah vs Nissan Serena: A Comprehensive Comparison • 03 Why Some Cars Are Cheap to Buy but Expensive to Maintain • 04 P0013 B Camshaft Position - Actuator Circuit (Bank 1) • 05 How to fix a car that's not shifting gears properly • 06 Air Suspension: Comprehensive Guide to Types, Benefits, and… • 07 The Complete Guide to the Major Parts of an Excavator • 08 Transmission Problems: Causes, Symptoms, and Solutions • 09 Why Your Car Interior Smells Different After Long Trips and… • 10 If You Can't Afford Repairs, You Can't Afford the Car •

DTC codes / C06xx · Brakes, steering and suspension / C066A

C066ARight Rear Wheel Speed Sensor B Intermittent/Erratic

C066A indicates that the anti-lock brake system (ABS) module has detected an intermittent or erratic signal from the right rear wheel speed sensor B circuit. The computer sets this code when the signal from that sensor drops out, jumps, or becomes inconsistent during driving, often without a permanent hard failure.

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

Symptoms you may notice

  • ABS warning light illuminated on the dashboard
  • Traction control or stability control warning light may also be on
  • Intermittent operation of the anti-lock braking system during hard stops
  • Speedometer fluctuation or inaccuracy if the sensor is used for vehicle speed
  • Often no symptoms besides the warning light, especially if the fault is momentary

Common causes, most likely first

  1. Damaged or chafed wiring harness at the right rear wheel, often near the suspension flex point
  2. Corroded or loose electrical connector at the sensor or ABS module
  3. Debris or metallic particles stuck to the sensor tip or tone ring
  4. Worn or damaged tone ring (reluctor wheel) on the right rear hub
  5. Failing wheel speed sensor itself, producing an intermittent signal
  6. Excessive wheel bearing play or hub runout affecting sensor air gap
  7. Electrical interference from aftermarket accessories or poor grounds

How to diagnose and fix it

  1. Inspect the right rear sensor wiring and connector for damage, corrosion, or loose pins; repair as needed
  2. Clean the sensor tip and tone ring of any debris or metallic buildup
  3. Check the tone ring for cracks, missing teeth, or excessive rust, and replace if damaged
  4. Measure the sensor air gap and compare to specification; adjust or replace the hub if out of range
  5. Perform a wiggle test on the harness while monitoring live wheel speed data to reproduce the intermittent fault
  6. Replace the right rear wheel speed sensor if all wiring and mechanical checks pass
  7. Clear the code and verify the repair with a road test, monitoring wheel speed PIDs for consistency

Intermittent wheel speed faults often misdiagnosed

  • A common mistake is replacing the sensor first when the real cause is a chafed wire inside the harness loom near the rear suspension, which only shorts when the suspension moves.
  • Metallic debris from a worn brake rotor or road grit can collect on the sensor magnet and cause erratic signals that mimic a failing sensor.
  • The code can be set by a loose or corroded ground connection for the ABS module, not just by the sensor circuit itself.
  • On some vehicles, the right rear wheel speed sensor also feeds the speedometer, so an intermittent signal can cause cruise control dropout or transmission shift issues without any ABS warning.
  • A failing wheel bearing can create enough play to change the sensor air gap dynamically, setting an intermittent code that returns even after sensor replacement.

Can I keep driving with C066A?

The vehicle remains safe to drive under normal conditions because the base brakes still work, but avoid hard braking or emergency maneuvers until the fault is repaired, as ABS may not engage reliably. If the warning light is accompanied by a loss of speedometer or other systems, have it checked promptly.

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.

Running on fumes Free guides aren't free to make. Top up the tank. Any amount, one time. Fuel the Garage