Code C0660 indicates the ABS control module has detected a range or performance issue with the left rear wheel speed sensor circuit designated as 'B' (typically a second sensor on the same wheel or a specific sensor in a dual-sensor setup). The signal from this sensor is outside expected parameters, intermittent, or does not correlate with other wheel speed inputs during vehicle operation.
The sensor element itself has failed open, shorted, or drifted out of specification due to age, heat cycling, or internal contamination.
Chafed, broken, or corroded wires or terminals between the sensor and the ABS module create high resistance, shorts, or intermittent connections.
The sensor is not seated fully, the mounting bracket is bent, or debris has accumulated, increasing the gap between the sensor and the tone ring beyond specification.
Missing, cracked, or rust-clogged teeth on the tone ring produce an erratic or weak signal that fails range/performance checks.
The module's input circuitry for sensor B has failed, though this is far less common than sensor or wiring faults.
No. The ABS module is rarely the root cause; the sensor, its wiring, the tone ring, or mounting issues account for the vast majority of C0660 occurrences. Module replacement should only be considered after all external circuit and mechanical checks pass.
The vehicle remains drivable, but ABS, traction control, and stability control will be disabled or limited, increasing stopping distance on slippery surfaces and reducing emergency handling capability. Repair should be scheduled promptly.
Some vehicles use two independent wheel speed sensors at the left rear (e.g., one for ABS and one for stability control, or a primary/backup arrangement). 'Sensor B' identifies the specific circuit the module has flagged.
Not if the underlying issue is wiring damage, a faulty tone ring, incorrect air gap, or a connector problem. The sensor is the most likely failure point, but thorough circuit and mechanical verification prevents unnecessary replacement.