C0666 indicates the ABS/control module has detected an open circuit in the "B" wheel-speed-sensor circuit for the right rear wheel. An open circuit means electrical continuity is broken somewhere between the sensor and the module, so the system cannot read that wheel's speed reliably. The result is usually an illuminated ABS, traction-control, or stability-control warning.
The sensor coil or internal circuit can open with age, heat, or vibration, producing a circuit-open code even if the wiring looks intact.
Rear wheel-speed harnesses flex and run near suspension components, so broken wires or rubbed-through insulation are common sources of an open circuit.
Water, salt, or vibration can degrade terminals and create high resistance or a complete open across the sensor circuit.
A loose sensor, missing mounting hardware, or a cracked tone ring can change air-gap enough to make the module interpret the signal as an open or missing circuit.
If the sensor, wiring, and connectors all test good, the module's input circuit could be failing, but this is a genuinely uncommon cause for a single-circuit open code.
The vehicle is usually drivable, but ABS, traction control, and/or stability control may be disabled or operate in a limited mode. It should be diagnosed promptly, especially in wet or slippery conditions.
Usually not. This code most often traces to a failed sensor, damaged wiring, or a corroded connector. Replacing the ABS module should only be considered after sensor and wiring faults are genuinely ruled out.
It is possible but less likely. A damaged tone ring or incorrect gap more commonly causes erratic or weak signals; an open-circuit code usually points to the sensor or wiring itself.
The 'B' designation identifies a specific sensor circuit or a redundant sensor channel used by the manufacturer for that wheel. It is not necessarily a second physical wheel.