OBD-II code · Powertrain (generic)
P0509 Idle Air Control System Circuit High
Same as P0508 with the line shorted to supply or open. Wiring faults of this kind typically come from chafing, water ingress at connector seals, or pin push-back — a wiggle test on the harness while the code is active often confirms the location.
Is it safe to drive with P0509?
Usually safe to drive in the short term. Get it diagnosed when convenient, sooner if the car drives differently.
Common causes
- Most likelyControl line shorted to supply
- PossibleOpen in IAC valve or harness
- Less likelyConnector pins corroded - high contact resistance
Symptoms
- Check engine light on
- Idle speed too high, too low, or unstable
- Possible stalling at idle or after cold start
Repair at a glance
- Difficulty
- Easy
- DIY friendly
- Often, with basic tools
- Typical labour
- 0.4–1.5 h
- Emissions test
- Usually unaffected
- Parts involved
- Idle Air Control Valve, Iac Wiring
Related codes
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.