Damaged or corroded wiring harness at the right rear wheel, often from road debris or chafing; Failed right rear wheel speed sensor due to heat, contamination, or physical damage; Open circuit in the sensor pigtail or connector, such as a broken wire or pushed pin; Corroded or loose electrical connector at the sensor or ABS module; Internal fault in the ABS control module affecting the sensor circuit; Debris or metallic particles on the sensor tip or tone ring interfering with signal; Aftermarket or incorrect sensor installed that does not meet specifications

DTC codes / C06xx · Brakes, steering and suspension / C0666

C0666Right Rear Wheel Speed Sensor B Circuit/Open

Q: What does code C0666 mean?

Right Rear Wheel Speed Sensor B Circuit/Open. C0666 indicates that the anti-lock brake system (ABS) control module has detected an open circuit or abnormal voltage on the right rear wheel speed sensor's 'B' circuit, which is typically the signal return or second wire in a two-wire sensor design. The module monitors the sensor's electrical integrity and sets this code when the circuit does not behave as expected, which can disable ABS and traction control functions.

C0666 indicates that the anti-lock brake system (ABS) control module has detected an open circuit or abnormal voltage on the right rear wheel speed sensor's 'B' circuit, which is typically the signal return or second wire in a two-wire sensor design. The module monitors the sensor's electrical integrity and sets this code when the circuit does not behave as expected, which can disable ABS and traction control functions.

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 also on
ABS and traction control systems disabled, increasing stopping distance in slippery conditions
Often no symptoms besides the warning light, with normal braking performance in dry conditions
Intermittent warning light that comes and goes with vibration or moisture
Possible speedometer inaccuracy if the affected sensor also feeds the speed signal

Common causes, most likely first

Damaged or corroded wiring harness at the right rear wheel, often from road debris or chafing
Failed right rear wheel speed sensor due to heat, contamination, or physical damage
Open circuit in the sensor pigtail or connector, such as a broken wire or pushed pin
Corroded or loose electrical connector at the sensor or ABS module
Internal fault in the ABS control module affecting the sensor circuit
Debris or metallic particles on the sensor tip or tone ring interfering with signal
Aftermarket or incorrect sensor installed that does not meet specifications

How to diagnose and fix it

Inspect the right rear wheel speed sensor and its wiring for visible damage, corrosion, or loose connections
Disconnect the sensor connector and check for bent pins, water intrusion, or green corrosion
Measure the sensor's resistance with a multimeter and compare to manufacturer specifications
Check the sensor's AC voltage output while spinning the wheel by hand, looking for a consistent waveform
Perform a wiggle test on the harness while monitoring sensor signal on a scan tool to detect intermittent opens
Inspect the tone ring for cracks, missing teeth, or debris buildup and clean or replace as needed
If all external checks pass, test continuity from the sensor connector to the ABS module to rule out an open circuit

What the B circuit really monitors

The 'B' circuit designation often refers to the signal return wire, so an open there can mimic a failed sensor even when the sensor itself tests good.
A common misdiagnosis is replacing the sensor when the real fault is a corroded connector pin or chafed wire hidden behind the wheel well liner.
On some vehicles, the right rear sensor shares a ground with other components, so a bad ground can set this code along with others.
The ABS module may set this code intermittently if the harness is stressed by suspension movement, so always wiggle-test the wiring while watching live data.
After any repair, the ABS module may need a recalibration or a drive cycle to clear the code and restore full function.

Can I keep driving with C0666?

You can usually drive the vehicle with this code, but ABS and traction control will be disabled, so exercise extra caution in wet, icy, or loose-surface conditions and avoid hard braking. Have the fault diagnosed soon to restore 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.