C0501 indicates the vehicle’s left‑front wheel speed sensor is reporting a signal that is outside the expected range. The ABS/ESC system cannot reliably use the sensor data for traction or stability control.
The sensor element or its internal circuitry has failed, producing voltage or frequency outside the calibrated range.
Frayed harness, broken pins, or moisture in the connector can cause intermittent or out‑of‑range signals.
If the sensor is too far from or too close to the tone ring, the generated pulses will be too weak or too strong for the controller.
A cracked, missing, or heavily corroded tone ring will produce irregular pulse patterns that the controller flags as out of range.
Very rarely, the ABS control unit itself may misinterpret a valid sensor signal; this is a last‑resort diagnosis after all hardware checks are cleared.
In practice the PCM (engine control module) does not process wheel‑speed data for this code; the ABS/ESC module does. Replacing the PCM will not resolve C0501.
If corrosion or dirt is present, cleaning the connector can restore proper signal and clear the code, but only if the sensor itself is still functional.
Replacing the ABS module is rarely needed. It should be considered only after the sensor, wiring, and tone ring have been verified as good and the code persists.
The vehicle will still be drivable, but anti‑lock braking and traction‑control functions may be disabled, reducing safety in slippery conditions.