P0502: Vehicle Speed Sensor A Circuit Low Input

What does P0502 mean?

Vehicle speed input A is lower than expected or missing when the vehicle should be moving. The computer may lose information needed for shifting or stability-related functions.

Generic OBD-II definition: Vehicle Speed Sensor A Circuit Low Input. Confirm applicability in your vehicle service information.

Common causes

• Speed-signal wiring fault
• Failed sensor or metal debris at the pickup
• Damaged reluctor teeth

Symptoms

• Speedometer dropouts
• Harsh or irregular shifts
• ABS or traction warning lights

Diagnostic focus

Do not assume the car is safe simply because the engine runs well. Speed information may be used by braking and traction systems; investigate accompanying warnings.

Can I keep driving with P0502?

Severity: High Speed-data faults can affect shifting or driver-assistance functions. Stop if braking, traction control, or vehicle behavior feels unsafe and arrange prompt diagnosis.

If the check engine light is flashing or the car runs badly, stop driving and have it checked.

Typical fixes

• Compare scan speed with wheel or output-speed data
• Inspect the sensor and trigger wheel
• Test the low signal according to the correct sensor type

Sources & review

• OBD-Codes.com: P0502
• TroubleCodes.net: generic code definitions

Definitions and diagnostic background checked 2026-11-06. Generic guidance, not a substitute for the service procedure for your exact year, engine, and transmission.