The engine control module (ECM) controls the engine idle speed by adjusting the position of the idle air control (IAC) valve pintle. The IAC valve is a stepper motor driven by 2 internal coils. The movement of the IAC valve is controlled electrically by 4 circuits. Drivers within the ECM control the polarity of the 2 windings inside the IAC valve through these circuits. The ECM, by commanding the correct polarity in sequence, is able to command the motor within the IAC valve to rotate clockwise or counterclockwise in steps. In order for the armature of the stepper motor of the IAC valve to turn one revolution, it needs to move approximately 24 steps. The IAC valve motor is linked by a gear drive to the IAC valve pintle. The electrical pulses sent to the IAC valve coils, by the ECM, allows the pintle to extend or retract into the passage in the throttle body. By retracting the pintle, air is allowed to bypass the throttle valve, which will increase air flow and raise engine speed. When the pintle is extended, bypass air is decreased which lowers engine speed.

When the ignition switch is turned OFF for more than 10 seconds an IAC valve reset occurs. At that time, the ECM commands the IAC valve to extend for a certain period which allows the IAC pintle to seat in the throttle body bore. This position is then sensed as zero count position for the IAC valve by the ECM. It must be observed that the IAC valve position is only sensed by the ECM measuring counts or steps of the driver circuit, there is no direct sensing of its exact position. When this extend time period ends, the ECM then commands the IAC valve to retract a predetermined amount. This will allow for a high engine speed on the next ignition cycle. If for any reason the IAC valve pintle moves after this reset, before the next ignition cycle, the ECM will not be able to detect it and will affect the ability to control engine idle. When the IAC valve is removed for any reason the reset must be performed.

The ECM detects an open, short to ground or voltage on one of the IAC coil control circuits of the IAC valve.

DTC P0511 is a Type B DTC.

DTC P0511 is a Type B DTC.

Schematic Reference

Engine Controls Schematics

Electrical Information Reference

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

1. Engine running, observe the DTC information with a scan tool. DTC P0511 should not set.
2. Operate the vehicle within the Conditions for Running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.

1. Ignition OFF, disconnect the harness connector at the IAC valve.

Important: The ECM controls the IAC control circuits in pairs. One pair will be grounded, while the other pair is supplied a voltage.

2. Ignition ON, verify a test lamp illuminates between one pair of the following terminals and B+.

•	Terminals A and D

•	Terminals B and C

⇒	If the test lamp illuminates on a circuit other than a circuit in the pair, test the isolated circuit for a short to ground. If the circuit tests normal, replace the ECM.

⇒	If the test lamp does not illuminate on both circuits in the pair, test the applicable control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the ECM.

3. Verify a test lamp illuminates between one pair of the following terminals and ground.

•	Terminals A and D

•	Terminals B and C

⇒	If the test lamp does not illuminate on both circuits in the pair, test the control circuits for a short to ground or an open/high resistance. If the circuit tests normal, replace the ECM.

Important: The ECM will reverse the polarity of each circuit pair after a key cycle.

4. Ignition OFF for 20 seconds. Ignition ON, repeat steps 2 and 3 in order to verify all circuits test normal.
5. If all circuits test normal, inspect for the following:

•	A clogged IAC passage

•	Excessive deposits on the throttle plate or bore

•	Excessive deposits on IAC valve pintle or bore

•	Restricted air intake system

•	The throttle body for damage and/or tampering

•	Vacuum leaks

•	Malfunctioning PCV valve

6. If all conditions test normal, test or replace the IAC valve.

1. Ignition OFF, disconnect the harness connector at the IAC valve.
2. Test for 40-80 ohms of resistance between the following terminals:

•

A and B

•

C and D

⇒	If not within the specified range, replace the IAC valve.

3. Test for infinite resistance between the following terminals:

•

A and C

•

B and C

⇒	If less than the specified value, replace the IAC valve.

4. Test for infinite resistance between each terminal and the IAC valve housing.

⇒	If less than the specified value, replace the IAC valve.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for engine control module replacement, setup, and programming