P0501: OBD-II code P0501 flags an implausible vehicle speed signal — the PCM sees a speed reading that doesn't correlate with engine RPM and gear.

Symptoms

• Check engine light is on; speedometer may fluctuate or drop out intermittently.
• Cruise control may drop out or refuse to engage, and the transmission may shift erratically.
• The ABS lamp can illuminate on vehicles where wheel speed feeds the VSS calculation.

Common causes

• A failed vehicle speed sensor with intermittent output or a drifting signal.
• Damaged wiring or a corroded connector at the VSS or the ABS module.
• Mismatched tyre sizes or an aftermarket wheel/tyre combination skewing the speed calculation.

What to do?

Compare live VSS to actual road speed with a scan tool. Inspect the sensor connector for corrosion. Replace the sensor if the signal is intermittent. Verify tyre sizes match manufacturer spec.