Idle Air Control System Circuit Low

What it means

P0508 is stored when the engine control module measures a voltage in the Idle Air Control System 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 Idle Air Control System circuit
2. Corroded, loose or water-damaged connector terminals
3. Failed Idle Air Control System 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 Idle Air Control System 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 Idle Air Control System 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

• P0507Idle Air Control System RPM Higher Than Expected
• P0509Idle Air Control System Circuit High
• P0506Idle Air Control System RPM Lower Than Expected
• P0510Closed Throttle Position Switch
• P0505Idle Air Control System
• P0511Idle Air Control Circuit
• P0504Brake Switch 'A'/'B' Correlation
• P0512Starter Request Circuit