Vehicle Speed Sensor 'A' Circuit Low Input

What it means

P0502 is stored when the engine control module measures a voltage in the Vehicle Speed Sensor 'A' circuit that stays below the expected minimum. In practice this points to a short to ground, a damaged wire or a failed component rather than a mechanical problem.

This entry is compiled automatically from the standard definition and typical diagnostic practice for this type of fault. A detailed, reviewed article is in preparation.

Symptoms

• Check engine light on
• Idle too high, too low or hunting
• Stalling when coming to a stop
• Speedometer or cruise control not working in some cases

Common causes

1. Damaged, chafed or corroded wiring in the Vehicle Speed Sensor 'A' circuit
2. Corroded, loose or water-damaged connector terminals
3. Failed Vehicle Speed Sensor 'A' component (sensor, solenoid or actuator)
4. Poor ground connection for the module or component
5. Faulty control module driver (rare, confirm all else first)

How to diagnose

1. Read freeze frame data and note when the code set (cold start, under load, after rain)
2. Inspect the Vehicle Speed Sensor 'A' connector for bent pins, corrosion and water; wiggle the harness with the engine running and watch live data
3. Measure supply voltage and ground at the connector with the key on
4. Check the signal wire for shorts to ground or battery and for continuity to the control module
5. Test or substitute the Vehicle Speed Sensor 'A' only after wiring and connectors are confirmed good
6. Clear the code and complete a drive cycle to confirm the repair

Related codes

Nearby codes in this group

• P0501Vehicle Speed Sensor A Range/Performance
• P0503Vehicle Speed Sensor 'A' Intermittent/Erratic/High
• P0500Vehicle Speed Sensor 'A'
• P0504Brake Switch 'A'/'B' Correlation
• P0505Idle Air Control System
• P0506Idle Air Control System RPM Lower Than Expected
• P0507Idle Air Control System RPM Higher Than Expected
• P0508Idle Air Control System Circuit Low