OBD-II Trouble Code Description for P0511 GMC

Idle Air Control Circuit

What does this mean?

OBD2 Code P0511 GM definition:
This system automatically controls engine idle speed to a specified level. Idle speed is controlled through fine adjustment of the amount of air which by-passes the throttle valve via Idle Air Control Valve (IACV) and Auxiliary Air Control (AAC) Valve. The IACV-AAC valve changes the opening of the air by-pass passage to control the amount of auxiliary air. This valve is actuated by a step motor built into the valve, which moves the valve in the axial direction in steps corresponding to the ECM output signals. One step of IACV-AAC valve movement causes the respective opening of the air by-pass passage. (i.e. when the step advances, the opening is enlarged.) The opening of the valve is varied to allow for optimum control of the engine idling speed. The crankshaft position sensor (POS) detects the actual engine speed and sends a signal to the ECM. The ECM then controls the step position of the IACV-AAC valve so that engine speed coincides with the target value memorized in ECM. The target engine speed is the lowest speed at which the engine can operate steadily. The optimum value stored in the ECM is determined by takig into consideration various engine conditions, such as during warm up, deceleration, and engine load (air conditioner, power steering and cooling fan operation).

Symptoms

Possible sumptoms of OBD code P0511 GM
– Engine Light ON (or Service Engine Soon Warning Light) – Engine hard to start – Rough or erratic idle speed

Causes

Possible causes of OBD code P0511 GM
– The IACV-AAC valve Harness or connectors circuit is open or shorted – Faulty IACV-AAC valve The Error code is generally activated on detection of the following conditions: The P0511 GM code is set when the IACV-AAC valve does not operate properly.

Possible Solutions