P0511Idle Air Control Circuit
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Needs a drive cycle to confirm a fix
- How the car detects it
- CARB requires the idle speed control to be monitored: petrol 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. P0511 is the general circuit fault of the idle valve – open, short to ground or to positive – without separating low and high, which CARB permits. Ford (up to about 2012, engines with an idle valve) has the output stage report it via a diagnostic status bit, continuously. Valve types are PWM solenoid or rotary valves (two wires) or stepper motors (four wires, typical of GM). Without a working valve the engine runs on a fixed bypass or the mechanical stop and may stall.
- What you may notice
- Idle too high, too low or fluctuating
- Engine stalls at idle
- Check engine light on
- Likely causes
- LikelyIdle valve faulty (coil open or shorted)
- PossibleWire open or shorted
- PossibleConnector corroded, pins pushed back
- RareDriver in the engine module
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Often possible to do yourself.Typical cost: €50 – €350
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.