Circuit Description
The Powertrain Control Module (PCM) controls the air entering into the engine with an idle air control (IAC) valve. To increase the idle RPM, the PCM commands the pintle inside of the IAC valve away from the throttle body seat. This allows more air to bypass through the throttle blade. To decrease the RPM, the PCM commands the pintle towards the throttle body seat. This reduces the amount of air bypassing the throttle blade. A scan tool will read the IAC valve pintle position in counts. The higher the counts, the greater the airflow that bypasses the throttle blade.
Conditions for Running the DTC
| • | DTCs P0105, P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0125, P0131, P0132, P0133, P0134, P0201, P0202, P0203, P0204, P0335, P0341, P0342, P0440, P0442, P0446, P0480, P0502, P0503, P0601, P0602, P1133, and P1441 are not set |
| • | The BARO is more than 72 kPa. |
| • | The engine coolant temperature (ECT) is more than 40°C (104°F). |
| • | The engine has been running more than 20 seconds. |
| • | The throttle position (TP) angle is less than 1 percent. |
Conditions for Setting the DTC
| • | The idle speed deviates above the desired RPM by more than 60 RPM for more than 5 seconds. |
| • | The IAC valve reads less than 2 counts on the scan tool for more than 13 seconds. |
Action Taken When the DTC Sets
| • | The malfunction indicator lamp (MIL) will illuminate after two consecutive ignition cycles in which the diagnostic runs with the malfunction present. |
| • | The PCM will record the operating conditions at the time that the diagnostic fails. This information will store in the Freeze Frame and Failure Records buffers. |
| • | A history DTC stores. |
| • | The coolant fan turns ON. |
Conditions for Clearing the MIL/DTC
| • | The MIL will turn OFF after three consecutive ignition cycles in which the diagnostic runs without a fault. |
| • | A history DTC will clear after 40 consecutive warm-up cycles without a fault. |
| • | Use the scan tool to clear the DTCs. |
Diagnostic Aids
| • | Inspect the IAC valve electrical connection for proper mating. |
| • | Inspect the wiring harness for damage. |
| • | Inspect for disconnected, cracked, or cut vacuum hoses. |
| • | Inspect the intake manifold and throttle body for leaks. |
| • | Inspect the intake manifold for cracks. |
| • | Refer to Rough, Unstable, or Incorrect Idle and Stalling . |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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The Powertrain On-Board Diagnostic (OBD) System Check prompts you to complete some basic diagnostics and to store the Freeze Frame and Failure Records data on the scan too, if applicable. This creates an electronic copy of the data that was captured when the malfunction occurred. The scan tool stores this data for later reference.
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A normally operating IAC system will be able to extend and retract by a scan tool and change the engine idle RPM. The valve movement is verified by an engine RPM change.
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If the scan tool was able to command the IAC valve smoothly, a malfunction may still exist internally within the IAC valve. Verify this by checking the internal resistance of the IAC valve.
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The IAC circuits always have ground or voltage signals in pairs. If the test lamp illuminates on more or less than two terminals, one of the circuits is shorted to voltage or open.
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The IAC circuits always have ground or voltage signals in pairs. If the test lamp illuminates on more or less than two terminals, one of the circuits is shorted to ground or open.
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The IAC circuits are constantly switched between ground and voltage. The test lamp should blink on all circuits when connected to a ground.
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A test lamp that remains ON constantly indicates that the circuit is shorted to voltage.
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Thoroughly inspect any suspected circuitry for the following conditions:
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Reprogram the replacement PCM and perform the crankshaft position system variation learn procedure. Refer to the latest Techline™ information for PCM programming.
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If no malfunctions are present at this point and no additional DTCs were set, refer to Diagnostic Aids for additional checks and information.
| • | Backed-out terminals |
| • | Improper mating |
| • | Broken locks |
| • | Improperly formed or damaged terminals |
| • | Faulty terminal-to wire connections |
| • | Physical damage to the wiring harness |
Step | Action | Value(s) | Yes | No | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | |||||||||
Does the engine RPM change smoothly when commanded by the scan tool? | 900-2,000 RPM | |||||||||
Are the resistances across terminals A and B, C and D within the specified value? | 40-80 ohms | |||||||||
4 |
Are the resistances across terminals B and C and terminals A and D infinite? | -- | ||||||||
Does the test lamp illuminate on 2 terminals? | -- | |||||||||
Does the test lamp illuminate on 2 terminals? | -- | |||||||||
Does the test lamp flash ON and OFF for all of the terminals? | -- | |||||||||
Did the test lamp remain ON constantly for the terminals that did not blink? | -- | |||||||||
9 |
Was a repair necessary? | -- | ||||||||
10 |
Was a repair necessary? | -- | ||||||||
Was a repair necessary? | -- | |||||||||
12 |
Was a problem found? | -- | ||||||||
13 |
Is the action complete? | -- | ||||||||
14 | Replace the IAC valve. Refer to the Idle Air Control Valve Replacement . Is the action complete? | -- | -- | |||||||
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Important: The replacement PCM must be reprogrammed.
Is the action complete? | -- | -- | ||||||||
16 |
Does the scan tool indicate that this diagnostic has run and passed? | -- | ||||||||
Check to see if any additional DTCs are set. Does the scan tool display any DTCs that you have not diagnosed? | Go to applicable DTC table | System OK |
