P0508 means Idle Air Control System Circuit Low. The idle air control valve circuit voltage is lower than expected. It is a generic OBD-II code, so the definition is the same on any make, but the most likely cause varies by engine; confirm with a scan tool and the service information for your vehicle before buying parts.
What P0508 means
Most vehicles built in the last two decades use electronic throttle control instead of a throttle cable: the accelerator pedal carries two or three position sensors, and the throttle body has a motor and two position sensors of its own. The computer compares the redundant sensors constantly, and any disagreement triggers reduced-power mode as a safety measure. Older engines with a throttle cable control idle with a separate idle air control valve.
P0508 symptoms
- Rough, low or unstable idle
- Stalling when coming to a stop
- Check engine light
Common causes of P0508
- Failed idle air control valve
- Wiring shorted to ground
- Connector fault
How to diagnose P0508
- Check the valve’s connector and wiring
- Measure valve resistance
- Command idle changes with a scan tool
Can you drive with P0508?
Usually yes, but expect stalling at stops.
P0508 tips
Carbon in the idle air passage can make the valve work harder; clean it while you have it out. If the valve’s resistance is in range and the wiring is good, check for a short to ground in the harness where it passes near the intake or throttle body.
Will P0508 clear itself?
If the fault stops, the computer turns off the check engine light by itself after several drive cycles without seeing it again, and the code stays in memory as history for a while. Clearing P0508 with a scan tool after a repair is fine, but if the cause is still there the code returns, sometimes within one drive. Disconnecting the battery also clears codes on most vehicles, but it erases learned fuel trims and idle settings as well.
Related codes
| Code | Meaning |
|---|---|
| P0505 | Idle Air Control System Malfunction |
| P0506 | Idle Air Control System RPM Lower Than Expected |
| P0509 | Idle Air Control System Circuit High |
Guides that help
When it is more than a sensor
Throttle and idle codes are fixed at the throttle body, the pedal, a sensor or a leak. If those check out and the engine still runs poorly, a compression test separates a control problem from a worn engine; compare engines by code on our engines page.
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