Damaged or corroded wheel speed sensor connector at the left front hub, often from road splash or debris; Broken, chafed, or stretched sensor wiring between the hub and the body harness, commonly at flex points; Failed left front wheel speed sensor itself, either an internal open winding or a cracked sensor body; Water or road salt intrusion into the sensor-to-harness connector causing high resistance or an open circuit; Loose or damaged sensor mounting bracket allowing the sensor to back away from the tone ring; Corroded or pushed-back terminals in the ABS module connector affecting the left front sensor circuit; Aftermarket or incorrectly routed replacement sensor wiring that does not match the original harness length or shielding

DTC codes / C06xx · Brakes, steering and suspension / C0651

C0651Left Front Wheel Speed Sensor B Circuit/Open

Q: What does code C0651 mean?

Left Front Wheel Speed Sensor B Circuit/Open. C0651 means the anti-lock brake system (ABS) control module has detected an open circuit or abnormal voltage on the left front wheel speed sensor's 'B' signal circuit. The module monitors the sensor's electrical loop and flags this code when the expected signal is missing, intermittent, or out of range, which prevents reliable wheel speed data for that corner.

C0651 means the anti-lock brake system (ABS) control module has detected an open circuit or abnormal voltage on the left front wheel speed sensor's 'B' signal circuit. The module monitors the sensor's electrical loop and flags this code when the expected signal is missing, intermittent, or out of range, which prevents reliable wheel speed data for that corner.

SystemChassis

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaBrakes, steering and suspension

Symptoms you may notice

ABS warning light illuminated on the dashboard, often accompanied by the traction control and stability control lights
No noticeable change in braking feel during normal driving, especially at low speeds
ABS may not activate during hard braking or slippery conditions, increasing stopping distance
Traction control or electronic stability control may be disabled, reducing intervention on low-grip surfaces
Intermittent warning light that comes and goes over bumps or during turns, pointing to a wiring fault
Speedometer or cruise control may behave erratically if the module shares wheel speed data with other systems

Common causes, most likely first

Damaged or corroded wheel speed sensor connector at the left front hub, often from road splash or debris
Broken, chafed, or stretched sensor wiring between the hub and the body harness, commonly at flex points
Failed left front wheel speed sensor itself, either an internal open winding or a cracked sensor body
Water or road salt intrusion into the sensor-to-harness connector causing high resistance or an open circuit
Loose or damaged sensor mounting bracket allowing the sensor to back away from the tone ring
Corroded or pushed-back terminals in the ABS module connector affecting the left front sensor circuit
Aftermarket or incorrectly routed replacement sensor wiring that does not match the original harness length or shielding

How to diagnose and fix it

Inspect the left front wheel speed sensor connector and wiring for corrosion, chafing, or a loose fit, and clean or repair as needed
Check the sensor's mounting and air gap to the tone ring, and verify the tone ring is clean and undamaged
Measure the sensor's resistance and compare it to the manufacturer's specification for that vehicle
Back-probe the sensor circuit at the ABS module connector and check for continuity and short-to-ground or short-to-power faults
Perform a wiggle test on the harness while watching live wheel speed data on a scan tool to catch intermittent opens
Replace the left front wheel speed sensor if resistance or signal testing confirms an internal fault
Clear the code and verify the repair by test-driving while monitoring left front wheel speed on the scan tool

What the B circuit really monitors

Many vehicles use a two-wire sensor where the 'B circuit' refers to the signal return or second wire, so a code for the B circuit can be set by a fault in the harness rather than the sensor itself.
A common misdiagnosis is replacing the sensor when the real problem is a corroded connector pin or a broken wire inside the loom near the strut tower.
Some ABS modules set C0651 only after an intermittent open is seen during a self-test at startup, so the fault may not be present when the vehicle is stationary.
Debris or a damaged tone ring can produce a signal that looks like an open circuit on a basic multimeter, so visual inspection of the ring is essential before condemning the sensor.
The code does not always mean the ABS is fully disabled; some systems retain normal braking but suspend ABS and stability functions, which drivers may not notice until an emergency stop.

Can I keep driving with C0651?

The vehicle remains safe to drive under normal conditions because base braking is unaffected, but avoid hard braking or slippery surfaces where ABS and stability control would normally intervene. Have the fault diagnosed promptly, since the loss of ABS can lengthen stopping distances in an emergency.

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.