For 1990-2009 cars

Table 1: | IAC Valve Terminal (Pin) Location

### Circuit Description

The powertrain control module (PCM) controls the idle air control (IAC) valve in order to regulate the air flow through the idle air bypass passage. The amount of air flowing through the idle air bypass passage determines the idle speed. The PCM directs the IAC valve according to changes in engine load. A stalling or poor idle concern could be caused by an IAC valve that is not operating properly.

### Diagnostic Aids

Any condition that can affect engine performance at idle, can affect the performance of the IAC system. A careful visual and/or physical inspection of the engine is necessary when the scan tool indicates that the engine speed or the IAC Motor Command readings are out of range.

A warm engine that is idling too slow, with a high IAC Motor Command of 50 percent or more, may have an open in the ignition positive voltage circuit to terminal 5.

A warm engine that is idling too fast, with a low IAC Motor Command of 15 percent or less, may have an open in the ignition positive voltage circuit to terminal 2.

An intermittent IAC system concern may be caused by poor electrical connections in the IAC valve circuits. Thoroughly check any circuitry that is suspected of causing an intermittent condition. Refer to Intermittent Conditions .

Use the following table in order to locate the correct terminals to test during diagnosis. The table layout corresponds to the pin location of the IAC valve electrical terminals.

#### IAC Valve Terminal (Pin) Location

Lock Tab
3 | 2 | 1
6 | 5 | 4

### Test Description

The numbers below refer to the step numbers in the diagnostic table.

1. The Diagnostic System Check-Engine Controls prompts the technician to complete some basic checks and store the Freeze Frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.

2. This step tests whether the PCM can operate the IAC valve with the scan tool. The IAC valve can be commanded to increase and/or decrease engine speed by using the scan tool RPM Control function. The RPM Control function of the scan tool is disabled when any DTCs are set, and when the engine is less than the normal operating temperature of 80°C (176°F).

3. This step checks the operation of the electrical load idle-up circuits. If there is no increase in the IAC Duty Cycle percentage when the accessory is turned on, the idle-up circuit may be inoperative or always on.

4. This step checks the operation of the A/C idle-up circuits. If there is no increase in the IAC Duty Cycle percentage when the A/C compressor is engaged, the idle-up circuit may be inoperative or always ON.

5. This step checks the electrical circuits between the IAC valve and the PCM.

6. This step determines whether the PCM is attempting to control the IAC valve. Each IAC coil control circuit should indicate a high voltage of 12 volts or more, and then a low voltage of 0.0-1.0 volts as the PCM commands changes in the engine speed. Remember to clear any DTCs and run the engine until the engine reaches a normal operating temperature before attempting RPM Control with the scan tool.

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
Schematic Reference:

#### Exhaust Gas Recirculation (EGR) Valve and EVAP Solenoids

Master Electrical Component List
Idle Air Control (IAC) Valve, Mass Air Flow (MAF) Sensor, Vehicle SPeED Sensor (VSS)
Data Link Connector (DLC) and Malfunction Indicator Lamp (MIL)
OBD II Symbol Description Notice
BATT, ABS, FI and ACC Fuses

1

Did you perform the Diagnostic System Check-Engine Controls?

--

Go to Step 2

Go to Diagnostic System Check - Engine Controls

2

Is there a Current or Pending DTC P0505 set?

--

Go to DTC P0505

Go to Step 3

3

1. Start the engine.
2. Run the engine until a normal operating temperature is reached.
3. Observe the Engine Speed and the IAC Motor Command parameters on the scan tool.

Are the Engine Speed and the IAC Motor Command within the specified ranges?

700-800 RPM in P/N

650-750 RPM in Drive

10-30% IAC Motor Command

Go to Step 5

Go to Step 4

4

1. Operate the engine at a normal operating temperature.
2. Select RPM Control, under IAC System, in the Special Functions menu of the scan tool.
3. Command the IAC valve to increase and decrease the engine speed with the scan tool.

Did the engine speed increase and decrease as commanded by the scan tool?

--

Go to Step 5

Go to Step 8

5

1. Start the engine.
2. Place the transmission in Park or Neutral.
3. Operate the following accessories, one at a time, while observing the Engine Speed and the IAC Motor Command parameters on the scan tool:

• | Turn ON the headlights

• | Turn ON the HVAC blower motor, leaving the A/C Off

• | Turn ON the rear window defogger, if equipped

Does the Engine Speed stay within the specified range while the IAC Motor Command increases 2 to 3 percent?

700-800 RPM in P/N

Go to Step 6

Go to Electrical/Accessory Load Idle-Up Signal Diagnosis

6

Turn ON the HVAC blower motor and the air conditioning, if equipped.

Is the Engine Speed within the specified range and does the IAC Motor Command increase 4 to 12 percent when the A/C compressor is operating?

750-850 RPM in P/N

Go to Step 7

Go to Electrical/Accessory Load Idle-Up Signal Diagnosis

7

1. Turn OFF all accessories.
2. Ensure that the engine is operating at a normal temperature.
3. Observe the Engine Speed and the IAC Motor Command parameters on the scan tool.

Are the Engine Speed and the IAC Motor Command within the specified ranges?

700-800 RPM in P/N

650-750 RPM in D

10-30% IAC Motor Command

System OK

Go to Rough, Unstable, or Incorrect Idle and Stalling

8

1. Turn OFF the ignition.
2. Disconnect the IAC valve electrical connector.
3. Use a digital multimeter (DMM) to measure the resistance of the following IAC valve coil windings:

• | Between pin 1 and pin 2

• | Between pin 2 and pin 3

• | Between pin 5 and pin 6

• | Between pin 4 and pin 5

4. Refer to the IAC Valve Terminal Identification table in Diagnostic Aids.

Are the resistances within the specified range?

35-43 ohms at 20°C (68°F)

Go to Step 9

Go to Step 15

9

1. Turn ON the ignition, leaving the engine OFF.
2. Probe both ignition positive voltage circuits of the IAC valve on the harness side with a test lamp connected to ground.

Did the test lamp illuminate on both circuits?

--

Go to Step 10

Go to Step 12

10

1. Turn OFF the ignition.
2. Connect the IAC valve electrical connector.
3. Disconnect the PCM electrical connector C4.
4. Turn ON the ignition, leaving the engine OFF.
5. Measure the voltage of each IAC coil control circuit at the harness side of the PCM connector C4 with a DMM connected to ground.

Is the voltage of each circuit more than the specified value?

12 V

Go to Step 11

Go to Step 13

11

1. Turn OFF the ignition.
2. Connect the PCM electrical connector C4.
3. Start the engine.
4. Run the engine until a normal operating temperature is reached.
5. Backprobe each IAC coil control circuit at the PCM with a DMM connected to ground.
6. Observe the voltage display on the DMM for each IAC coil control circuit while increasing and decreasing the engine speed with the scan tool RPM Control function.

Does the voltage of circuit switch from high to low with the increase and decrease in the engine speed?

--

Go to Step 14

Go to Step 16

12

Repair the high resistance or the open in the ignition positive voltage circuit. Refer to Wiring Repairs in Wiring Systems.

Is the action complete?

--

Go to Step 17

--

13

Repair the short to ground, open circuit, or high resistance in any IAC coil control circuit that did not measure at least 12 volts in step 10. Refer to Wiring Repairs in Wiring Systems.

Is the action complete?

--

Go to Step 17

--

14

1. Remove the IAC valve. Refer to Idle Air Control Valve Replacement .
2. Inspect the idle air passage for restrictions or blockage.
3. Repair as necessary.

Was a repair necessary?

--

Go to Step 17

Go to Step 15

15

Replace the IAC valve. Refer to Idle Air Control Valve Replacement .

Is the action complete?

--

Go to Step 17

--

16

Replace the PCM. Refer to Powertrain Control Module Replacement .

Did you complete the replacement?

--

Go to Step 17

--

17

Operate the vehicle within the conditions in which the customer concern was first noticed.

Is the concern still present?

--

Go to Diagnostic Trouble Code (DTC) List

System OK