Idle Air Control System Circuit Low
What does P0508 mean?
The P0508 code means the vehicle's onboard diagnostic system has detected: Idle Air Control System Circuit Low. This is a moderate severity code.
Common Symptoms
- Engine stalling at idle
- Very low idle RPM
- Rough or unstable idle
- Engine dies when foot is removed from gas pedal
- Check engine light on
Probable Causes (Ranked by Likelihood)
- Faulty idle air control (IAC) valve Very High
- Open or short to ground in IAC circuit wiring High
- Corroded IAC valve connector Moderate
- Carbon buildup restricting IAC valve movement Moderate
- PCM driver circuit failure Low
Step-by-Step Diagnostic Procedure
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Check IAC valve connector for corrosion, bent pins, or loose connections
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Measure IAC valve coil resistance -- typical spec is 10-14 ohms between terminals
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Test IAC control circuit for shorts to ground -- disconnect IAC and measure wiring resistance to ground
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Command IAC valve open and closed with a scan tool -- listen for clicking or movement
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Remove IAC valve and inspect the pintle for carbon buildup -- clean with throttle body cleaner
Frequently Asked Questions
Can I drive with code P0508?
Yes, but the engine may stall unexpectedly at idle, such as at stop signs or in traffic. You may need to keep your foot on the gas slightly to prevent stalling. This can be a safety concern in heavy traffic.
What does circuit low mean for the IAC?
Circuit low means the PCM detects lower than expected voltage or resistance on the IAC control wire. This typically indicates the IAC valve is stuck, the wiring has a short to ground, or the IAC valve coil has an internal fault.
Can I clean the IAC valve instead of replacing it?
Yes, cleaning the IAC valve with throttle body cleaner often resolves the issue when carbon buildup is the cause. Remove the valve, spray the pintle and bore thoroughly, allow it to dry, and reinstall. If cleaning does not resolve the code, replacement is needed.