What P0511 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 %.
How the engine computer detects it
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.
Written from public technical sources and not yet checked by a mechanic. How we write these pages
Symptoms
- Idle too high, too low or fluctuating
- Engine stalls at idle
- Check engine light on
Common causes
- Idle valve faulty (coil open or shorted) Most likely
- Wire open or shorted Possible
- Connector corroded, pins pushed back Possible
- Driver in the engine module Less likely
How to diagnose P0511
- Read every stored code with an OBD-II scanner. If misfire or fuel trim codes are there too, fix those first: they often cause this one.
- Inspect the parts involved: idle air control valve, valve wiring, engine control module.
- Work through the causes above from most to least likely, cheapest checks first.
- Clear the code and drive a full drive cycle to confirm the repair held.
Reading the code
- P
- Powertrain
- 0
- Generic (SAE) code
- 5
- Vehicle speed, idle control and auxiliary inputs
- 11
- Specific fault
Questions drivers ask
Can I drive with code P0511?
Usually yes for a short time, if the car drives normally, the temperature gauge reads normal and the check engine light is steady. If the light flashes, the engine loses power or overheats, or other warning lights come on, pull over and have it checked.
Will my car pass an emissions inspection with P0511?
Probably not in states that test vehicles with an OBD-II scan: an emissions-related code that keeps the check engine light on is usually an automatic fail. Rules differ by state and county, so check yours.
Will P0511 clear by itself?
The light can go off after several drive cycles without the fault, but the code returns if the cause is still there. After a repair, the readiness monitors need a full drive cycle before an inspection.
Can I fix P0511 myself?
Often yes, with an OBD-II scanner and basic tools. Difficulty: medium. Start with the cheapest checks before replacing expensive parts.
This page is general information, not a substitute for a professional diagnosis. Repair costs are rough estimates for parts and labor and vary by vehicle and region.