| 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.
Lock Tab | ||
3 | 2 | 1 |
6 | 5 | 4 |
Test Description
The numbers below refer to the step numbers in the diagnostic table.
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A 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.
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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).
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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.
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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.
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This step checks the electrical circuits between the IAC valve and the PCM.
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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: Engine Controls Schematics | ||||||||||||
Did you perform A Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | ||||||||||
2 | Use a scan tool and check for IAC system DTCs. Is a DTC P0505, DTC P0506, or DTC P0507 set? | -- | Go to Step 3 | |||||||||
3 |
Are the Engine Speed and the IAC Motor Command within the specified ranges? | 700-800 RPM in P/N 10-50% IAC Motor Command | Go to Step 5 | Go to Step 4 | ||||||||
Did the engine speed increase and decrease as commanded by the scan tool? | -- | Go to Step 5 | Go to Step 8 | |||||||||
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 | ||||||||||
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 | ||||||||||
7 |
Are the Engine Speed and the IAC Motor Command within the specified ranges? | 700-800 RPM in P/N 10-50% IAC Motor Command | System OK | |||||||||
8 |
Are the resistances within the specified range? | 21-23 ohms at 20°C (68°F) | Go to Step 9 | Go to Step 15 | ||||||||
9 |
Did the test lamp illuminate on both circuits? | -- | Go to Step 10 | Go to Step 12 | ||||||||
Is the voltage of each IAC Coil Control circuit near the specified value? | B+ | Go to Step 11 | Go to Step 13 | |||||||||
Does the voltage of the 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. Did you complete the repair? | -- | 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 B+ in step 10. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 17 | -- | ||||||||
14 |
Was a repair necessary? | -- | Go to Step 17 | Go to Step 15 | ||||||||
15 | Replace the IAC valve. Refer to Idle Air Control Valve Replacement . Did you complete the repair? | -- | Go to Step 17 | -- | ||||||||
16 |
Important: The replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the repair? | -- | Go to Step 17 | -- | ||||||||
17 | Operate the vehicle within the conditions in which the customer concern was first noticed. Is the concern still present? | -- | System OK | |||||||||
