OBD-II code C0651 indicates an open circuit in the left-front wheel-speed sensor B circuit. This means the anti-lock brake system (ABS) or traction/stability control module has detected no signal from the secondary (B) wire of the left-front wheel-speed sensor.
The most common cause is chafed, pinched, or broken wires between the sensor and the ABS module, often near the wheel hub or suspension components.
The sensor itself may have failed due to internal damage, corrosion, or excessive debris buildup on the reluctor ring.
Moisture intrusion or vibration can cause poor electrical contact at the sensor or ABS module connector, leading to an open circuit.
A cracked, missing, or excessively worn reluctor ring can prevent the sensor from generating a proper signal, though this usually causes intermittent or weak signals rather than a complete open.
While rare, an internal open in the ABS module or a broken trace on the circuit board can cause this code. This is uncommon compared to external wiring or sensor issues.
While the vehicle may still be drivable, the ABS, traction control, and stability control systems will likely be disabled. This increases stopping distances and reduces control in slippery conditions. Have the issue diagnosed and repaired promptly.
No. The ABS module is rarely the cause of this code. In the vast majority of cases, the issue is due to damaged wiring, a faulty sensor, or a corroded connector. Replace the module only after verifying all other potential causes.
Many vehicles use a dual-circuit wheel-speed sensor design for redundancy and to detect faults. The ABS module compares signals from both circuits to ensure accuracy and reliability. An open in either circuit will trigger a code.
A severely worn or failed wheel bearing can sometimes damage the reluctor ring or cause the sensor to become misaligned, leading to a weak or no signal. However, this typically results in intermittent or erratic codes rather than a consistent open circuit.