For 1990-2009 cars

### Circuit Description

The IAC system controls the idle speed by allowing a controlled amount of air to bypass the throttle blade via a passage in the IAC valve. One of the ECM's uses for the IAC system is to maintain a desired idle speed, which can vary depending on input to the ECM and other criteria. If the ECM detects that the engine speed is outside of the IAC system's range of control at idle, a DTC will set.

### Conditions for Running the DTC

• | The following DTCs are not set: P0100, P0115, P0116, P0120, P0440, P0441, P0443, P0501, P0505.

• | The IAT is greater than -8.3°C (17°F).

• | The ECT is greater than 80.3°C (176.5°F).

• | The engine load is less than 2 milliseconds.

• | The EVAP diagnostic is not running.

• | The EVAP is not purging.

• | Vehicle speed = 0

### Conditions for Setting the DTC

• | The actual engine RPM is lower than the Desired Idle Speed by at least 100 RPM.

• | The Short Term Air Trim is greater than 5.6 g/s.

• | The above condition met for more than 10 seconds.

### Action Taken When the DTC Sets

The ECM illuminates the malfunction indicator lamp (MIL) and records the operating conditions in the Freeze Frame on the second consecutive drive trip that the diagnostic runs and fails.

### Conditions for Clearing the MIL/DTC

• | The ECM turns OFF the MIL after three consecutive drive trips that the diagnostic runs and passes.

• | A History DTC clears after forty consecutive warm-up cycles in which no failures are reported by this diagnostic or any other emission related diagnostic.

• | The ECM battery voltage is interrupted.

• | The scan tool clears the MIL/DTC.

### Diagnostic Aids

Use the Connector Test Adapter Kit J 35616 for any test that requires probing the ECM harness connector or a component harness connector. Using this kit will prevent damage to the harness connector terminals.

Check for the following conditions:

• | Poor connections at the ECM or at the component. Inspect the harness connectors for any backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection. Refer to Engine Control Module Diagnosis , Checking Terminal Contact for proper procedure.

• | Damaged harness. Inspect the wiring harness for any damage. If the harness appears to be OK, observe the scan tool while moving the related connectors and the wiring harnesses. A change in the display may help in order to locate the fault.

Refer to Symptoms for the Intermittents.

### Test Description

The number(s) below refer to the step number(s) on the Diagnostic Table.

Notice: Do not use any solvent that contains Methyl Ethyl Ketone (MEK). This solvent may damage fuel system components.

1. Verifies that the fault is currently present.

2. The IAC valve is very sensitive to dirt and other contaminants. If any contaminants are allowed to enter the air intake system, the IAC operation may be affected. Make sure that the ductwork and the air cleaner assembly are absolutely clean. Check the IAC valve for dirt contamination. Do Not immerse the IAC valve in carburetor cleaners or other chemical solvents. If deposits are present, clean the IAC shutter and air passages using a GM Top Engine Cleaner, P/N 1052626 or AC-Delco Carburetor Tune-Up Conditioner, P/N X66-P, or an equivalent product. The IAC valve should be blown out with compressed air and the shutter should be checked for free movement. If free movement of the shutter cannot be restored, replace the valve and gasket.

3. The IAC valve is very sensitive to dirt and other contaminants. If any contaminants are allowed to enter the air intake system, the IAC operation may be affected. Make sure that the ductwork and the air cleaner assembly are absolutely clean. Check the IAC valve for dirt contamination. Do Not immerse the IAC valve in carburetor cleaners or other chemical solvents. If deposits are present, clean the IAC shutter and air passages using a GM Top Engine Cleaner, P/N 1052626 or AC-Delco Carburetor Tune-Up Conditioner, P/N X66-P, or an equivalent product. The IAC valve should be blown out with compressed air and the shutter should be checked for free movement. If free movement of the shutter cannot be restored, replace the valve and gasket.

#### DTC P0506 - Idle Speed Low

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System check? | -- | Go to Step 2 | Go to Powertrain On Board Diagnostic (OBD) System Check
2 |

1. Start the engine.
2. Load the engine by turning on several accessories (e.g. A/C, headlights, rear defogger, etc.)

Is the actual engine speed no greater than 200 RPM above or 100 RPM below the Desired Idle Speed?

--

Fault not present. Go to Diagnostic Aids

Go to Step 3

3 | Is the engine RPM too high? | -- | Go to Step 4 | Go to Step 5
4 | Check for the following conditions:

• | Vacuum leaks

• | Throttle blade not closing properly

• | A damaged PCV system

• | A mechanical IAC valve failure

Is the action complete?

--

Go to Step 6

--

5 | Check for the following conditions:

• | Excessive deposits in the throttle body or the IAC valve/passages

• | A kinked or obstructed IAC air supply hose.

• | Mechanical IAC valve failure

• | A parasitic load on the engine (for example: a transmission problem, a belt driven accessory problem, etc.).

• | A mechanical engine problem (for example: an incorrect cam timing, etc.).

Is the action complete?

--

Go to Step 6

--

6 |

1. Clear the DTCs with the scan tool.
2. Turn off the ignition for 15 seconds.
3. Operate the vehicle with the conditions that are required for this vehicle to run. Refer to Conditions for Running the DTC.
4. Check for any DTCs.

Is this DTC set?

--

Go to Step 2

Go to Step 7

7 | Were there any additional DTCs noted during the Powertrain OBD System Check that have not been diagnosed? | -- | Go to the applicable DTC table | The System is OK