P0508 code meaning
Idle Air Control System Circuit Low
Powertrain system Generic code P05xx codes Check engine light
What P0508 means
CARB requires the idle speed control to be monitored: gasoline engines must flag a fault if the target idle speed is not reached within +200/−100 rpm, diesels within ±30 %. Older engines use a separate idle air control valve that bypasses the closed throttle; with electronic throttle the throttle itself controls idle and no separate valve exists. P0508 is an electrical fault in the drive circuit of a separate idle valve. Subaru (also in the Saab 9-2X) feeds the valve from the main relay and pulses it to ground; the module counts signal edges and sets P0508 at 8 or fewer in 64 ms instead of about 160 – the output hangs at one level – with the warning lamp at once and limp mode without idle control. Many makers, Ford among them, report all circuit faults under P0511 instead.
P0508 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyMedium, DIY possible
- Typical labor0.5 to 1.5 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P0508
- Idle fluctuates or is wrong
- Engine stalls at idle
- Check engine light on at once
Common causes of P0508
- Most likelyIdle valve coil faulty
- PossibleControl wire shorted to ground or open
- PossibleSupply missing (main relay, fuse)
- PossibleConnector contact at valve or module
- Less likelyDriver in the engine module
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Idle air control valveValve wiringEngine control module
What each part of P0508 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 5 | Area: vehicle speed, idle control and auxiliary inputs. |
| 08 | The exact fault in that area. |
What to do next
- Note P0508 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P0508
What does P0508 mean?
P0508 means "Idle Air Control System Circuit Low". CARB requires the idle speed control to be monitored: gasoline engines must flag a fault if the target idle speed is not reached within +200/−100 rpm, diesels within ±30 %. It is a generic code, so it means the same on every make.
Is it safe to drive with P0508?
Drive gently and only to a workshop. With P0508 the car can go into limp mode (reduced power) to protect itself.
Will P0508 fail an emissions test?
Yes, it can. P0508 is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P0508 to fix?
Difficulty: medium. A typical repair takes 0.5 to 1.5 hours of work. A careful DIY repair is possible with basic tools and a scanner.
Will P0508 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.