P0511 OBD-II Trouble Code: Idle Air Control Circuit

P0511 code definition

This DTC represents Idle Air Control Circuit, indicating an abnormal condition in the RPMs when the engine is idling.

What the P0511 code means

Each vehicle idles at a manufacturer specified RPM level. The PCM (powertrain control module) monitors the idle RPM to ensure that it falls within the expected parameters. If it doesn’t, then the PCM will attempt to return the RPMs to normal. Failing this, the DTC will set.

What causes the P0511 code?

The most common cause of this DTC is when the throttle body bore has carbon/coke buildup. Other possibilities include:

• A bad idle air control (IAC) valve or auxiliary air control (AAC) valve
• A short or open in the electrical circuit, such as a faulty IAC valve harness
• A severe vacuum leak
• A faulty PCM (rare)

What are the symptoms of the P0511 code?

The Malfunction Indicator Lamp (MIL) will likely come on, and the trouble code will be stored in the vehicle’s computer. In addition, you may notice high or low RPMs when the engine is idling, stalling at low speed, or intermittent stalling when the throttle is released.

How does a mechanic diagnose the P0511 code?

Diagnosing this condition may involve:

• Hooking the vehicle up to a scanner to record the data and identify any concurrent fault codes

• Clearing the DTCs out of the vehicle’s computer then road testing the vehicle to see if they return (in order to identify an intermittent condition)

• Visually inspecting the IAC wiring and connectors for damage or loose connections

• Using a scanner to manually open the IAC motor then testing the IAC motor connector voltage

• Inspecting the throttle body for coking and carbon buildup (coke will appear as a greasy black substance)

Common mistakes when diagnosing the P0511 code

Sometimes idle air control parts will be replaced without making sure the throttle body is not restricted. In attempting to repair the problem, throttle body cleaning can be an option, but more often than not the required chemicals damage the surrounding wiring and connectors. Replacement is usually the better option.

How serious is the P0511 code?

This fault is more than a convenience issue, due to the fact that the vehicle may not even be drivable. It is possible, however, that the car could stall unexpectedly, leaving you in a difficult or even unsafe situation. It’s best to have the problem looked at and repaired as soon as possible.

What repairs can fix the P0511 code?

Fixing an idle air control circuit malfunction may involve:

• Repairing any damaged wiring or connections
• Cleaning the throttle body bore or replacing the throttle body
• Repairing the IAC valve
• Diagnosing and repairing any concurrent DTCs

Need help with a P0511 code?

YourMechanic offers certified mobile mechanics who will come to your home or office to diagnose and repair your vehicle. Get a quote and book an appointment online or speak to a service advisor at 1-800-701-6230.