P0518 code meaning
Idle Air Control Circuit Intermittent
Powertrain system Generic code P05xx codes Check engine light
What P0518 means
Older engines without electronic throttle have a separate idle air control valve bypassing the closed throttle; CARB requires its output to be checked but not the fault types to be coded separately. P0518 means its circuit fails sporadically – the signal or current briefly leaves its valid range and returns. No manufacturer document available to us uses P0518; GM and Ford report idle valve faults as P0505–P0507 and P0511. Engines with electronic throttle do not set it.
P0518 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modeNot expected
- Repair difficultyEasy, DIY possible
- Typical labor0.5 to 2 hours
- Clears after repairAfter a drive cycle
Symptoms of P0518
- Fluctuating idle
- Engine stalls when coasting or stopping
- Check engine light (depending on the maker)
Common causes of P0518
- Most likelyLoose contact or corrosion at the idle valve connector
- PossibleBroken or chafed wire in the harness
- PossibleValve coil with shorted turns (temperature-dependent)
- 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 P0518 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. |
| 18 | The exact fault in that area. |
What to do next
- Note P0518 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 P0518
What does P0518 mean?
P0518 means "Idle Air Control Circuit Intermittent". Older engines without electronic throttle have a separate idle air control valve bypassing the closed throttle; CARB requires its output to be checked but not the fault types to be coded separately. It is a generic code, so it means the same on every make.
Is it safe to drive with P0518?
Usually yes, for a short time, if the check engine light is steady and the car drives normally. If the light flashes or the car runs badly, stop and have it checked.
Will P0518 fail an emissions test?
Yes, it can. P0518 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 P0518 to fix?
Difficulty: easy. A typical repair takes 0.5 to 2 hours of work. A careful DIY repair is possible with basic tools and a scanner.
Will P0518 clear itself after the repair?
After the repair the car has to complete a drive cycle (a mix of city and highway driving) before the test runs again. Until then the readiness monitor shows "not ready", which can fail an inspection.