P0508 moderate

Idle Air Control System Circuit Low

The P0508 code means the vehicle's onboard diagnostic system has detected: Idle Air Control System Circuit Low. This is a moderate severity code.

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Keep driving?: Yes, but fix soon
DIY difficulty: moderate
Estimated cost: $80 - $250 (parts and labor)

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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

Check IAC valve connector for corrosion, bent pins, or loose connections
Measure IAC valve coil resistance -- typical spec is 10-14 ohms between terminals
Test IAC control circuit for shorts to ground -- disconnect IAC and measure wiring resistance to ground
Command IAC valve open and closed with a scan tool -- listen for clicking or movement
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.