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 Setting the DTC
| • | DTC(s) P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0131, P0132, P0133, P0134, P0200, P0335, P0341, P0342, P0401, P0440, P0442, P0446, P0503, P1133, P1336, P1404 and P1441 are not set |
| • | The BARO is greater than 72 kPa. |
| • | The Engine Coolant Temperature (ECT) is greater than 40°C (104°F). |
| • | The engine RPM is above the desired RPM by more than 60 RPM for 13 seconds. |
| • | The engine has been running for more than 20 seconds. |
| • | The Throttle Position (TP) angle is less than 1 percent. |
| • | The IAC command is less than 2 counts. |
Action Taken When the DTC Sets
| • | The Malfunction Indicator Lamp (MIL) will illuminate after one consecutive ignition cycle in which the diagnostic runs with the fault being active. |
| • | The PCM will record the operating conditions at the time during which 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. |
| • | The MIL/DTCs can be cleared by using the scan tool. |
Diagnostic Aids
| • | Inspect the IAC valve electrical connection for proper mating. |
| • | Inspect the wiring harness for damage. |
| • | Inspect for a disconnected, cracked, or cut vacuum hoses. |
| • | Inspect for the proper installation of the crankcase ventilation valve. |
| • | Inspect the intake manifold and the throttle body for leaks. |
| • | Inspect the intake manifold for cracks. |
| • | Refer to Rough, Unstable, or Incorrect Idle and Stalling . |
Test Description
The number(s) below refer(s) to the step number(s) on the Diagnostic Table.
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The Powertrain OBD System Check prompts you to complete some of the basic checks and to store the freeze frame and failure records data on the scan tool if applicable. This creates an electronic copy of the data captured when the fault 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 fault may still exist internally within the IAC valve. You can 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 light illuminates on more or less than 2 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 light illuminates on more or less than 2 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 light should blink on all circuits when connected to ground.
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Thoroughly check any suspected circuitry for the following conditions:
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A test light that remains ON constantly indicates that the circuit is shorted to voltage.
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Reprogram the replacement PCM and perform the crankshaft position system variation learning procedure. Refer to the latest Techline information for PCM programming and Powertrain Control Module (PCM) for the crankshaft position system variation learning procedure.
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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 |
| • | Poor terminal to wiring 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? | 900-2000 RPM | |||
Are the resistances across terminals A and B, C and D within the specified value? | 40-80ohms | |||
4 |
Are the resistances across terminals B and C and terminals A and D infinite? | -- | ||
Does the test light illuminate on 2 terminals? | -- | |||
With a test light connected to B+, probe the IAC valve electrical connector terminals. Does the test light illuminate on 2 terminals? | -- | |||
7 | Check for an open or a short to ground in the IAC valve high and low circuits and repair the circuits as necessary. Was a repair necessary? | -- | ||
Does the test light flash ON and OFF for all of the terminals? | -- | |||
9 | Check for an open or a short to voltage in the IAC valve high and low circuits and repair the circuits as necessary. Was a repair necessary? | -- | ||
Check the PCM electrical connector for poor connections and repair the connector as necessary. Was a repair necessary? | -- | |||
11 | Inspect the IAC passages. Was a problem found? | -- | ||
Did the test light remain ON constantly for the terminals that did not blink? | -- | |||
13 | Replace the IAC valve. Is the action complete? | -- | -- | |
Replace the PCM. Is the action complete? | -- | -- | ||
15 |
Does the scan tool indicate that this diagnostic has ran 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 Refer to Diagnostic Aids |
