P0508
Idle Air Control System Circuit Low
Idle speed control
Generic OBD-II
High
What it means
P0508 means the idle-air control (IAC) circuit is reading lower voltage than expected, typically from a short to ground or a failing IAC valve. The IAC meters air around the throttle plate to hold a steady idle, so this fault often shows up as a rough idle or stalling when the engine drops to idle. It's worth fixing quickly because stalling can be unsafe.
High
Can I keep driving? Risky — a faulty idle-air control circuit can cause stalling at idle or in gear, so drive as little as possible until it's fixed.
Common symptoms
What you'll notice
- Check-engine light on
- Rough, low, or unstable idle
- Stalling at idle, at stops, or when coming to rest
- Hard to keep running right after start-up
Common causes
Most likely first
- Short to ground in the idle-air control (IAC) circuit wiringLikely
- Faulty IAC valve or motorCommon
- Corroded or loose IAC connectorCommon
- Carbon-clogged IAC passage restricting airflowLess often
- ECM driver fault (least common)Less often
How to diagnose & fix
Work through it in order
- Read freeze-frame data and note the idle conditions when the fault sets.
- Inspect the IAC connector and wiring for a short to ground, corrosion, or damage.
- Remove and inspect the IAC valve/passage for heavy carbon; clean or replace as needed.
- Measure the IAC circuit resistance and voltage against spec to confirm a valve vs. wiring fault.
- Replace the IAC valve if it tests bad; clear the code and confirm idle stabilizes.
FAQ
Quick answers
Is it safe to drive with P0508?+
Be cautious. A low IAC circuit can cause stalling at idle or when stopping, which is unsafe in traffic. Get it repaired promptly.
Can I just clear P0508?+
It clears, but returns quickly if the IAC valve, its passage, or the wiring is still faulty. Fix the cause first.
Related codes
Often seen with P0508
Read & clear P0508 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.
✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX