Circuit Description
The powertrain control module (PCM) controls the air entering into the engine with an idle control (IAC) valve. In order to increase the idle RPM, the PCM commands the pintle inside the IAC valve away from the throttle body seat. This allows more air to bypass through the throttle blade. In order 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 more air that is allowed to bypass the throttle blade.
Conditions for Running the DTC
| • | DTCs P0105, P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0125, P0131, P0132, P0133, P0134, P0200, P0335, P0341, P0342, P0440, P0442, P0446, P0480, P0502, P0503, P0601, P0602, P1133, and P1441are 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
| • | Engine RPM is below desired RPM by more than 100 RPM for 19 seconds. |
| • | IAC command is more than 145 counts. |
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. |
Diagnostic Aids
| • | Inspect the IAC valve electrical connection for proper mating. |
| • | Inspect the wiring harness for damage. |
| • | Inspect the throttle stop screw for signs of tampering. |
| • | Inspect the throttle linkage for signs of binding or excessive wear. |
| • | A slow or unstable idle may be the cause of one of the following conditions: |
| - | Fuel system to rich or to lean |
| - | Foreign material in the throttle body bore or in the air induction system |
| - | A leaking or restricted intake manifold |
| - | An excessive engine overloading: Check for seized pulleys, pumps, or motors on the accessory drive. |
| - | Too high a viscosity engine oil |
| • | 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 malfunction occurred. The scan tool stores this data for later reference.
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A normally operating IAC system will be able to be extended and retracted 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. You can check this by checking the internal resistance of the IAC valve.
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The IAC circuits always have ground or voltage signals on them in pairs. If the test light illuminates on more or less than 2 terminals, 1 of the circuits is shorted to voltage or open.
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The IAC circuits always have ground or voltage signals on them in pairs. If the test light illuminates on more or less than 2 terminals, 1 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 the voltage.
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Reprogram the replacement PCM and perform the crankshaft position system variation learn procedure. Refer to the latest Isuzu Technical Communications System (ITCS) information for PCM programming and Crankshaft Position System Variation Learn for the crankshaft position system variation learn procedure.
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If no malfunctions have been 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 the engine is commanded by the scan tool? | 900-2,000 RPM | |||||||||
Are the resistances across terminals A and B and terminals 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? | -- | |||||||||
Does the test light illuminate on 2 terminals? | -- | |||||||||
7 |
Was a repair necessary? | -- | ||||||||
Does the test light flash ON and OFF for all terminals? | -- | |||||||||
9 |
Was a repair necessary? | -- | ||||||||
Was a repair necessary? | -- | |||||||||
11 |
Was a problem found? | -- | ||||||||
Did the test light remain ON constantly for the terminals that did not blink? | -- | |||||||||
13 |
Is the action complete? | -- | -- | |||||||
Replace the PCM. Refer to the Powertrain Control Module Replacement . 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 Go to Diagnostic Aids |
