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 Setting the DTC
| • | DTCs P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0131, P0132, P0133, P0134, P0200, P0335, P0341, P0342, P0401, P0404, P0405, P0440, P0442, P0446, P0502, P0503, P1133, P1404 and P1441 not set |
| • | BARO is greater than 72 kPa. |
| • | Engine Coolant Temperature ( ECT) is greater than 40°C (104°F). |
| • | Engine RPM is below desired RPM by more than 60 RPM for 13 seconds. |
| • | Engine has been running more than 20 seconds. |
| • | Throttle Position (TP) angle is less than 1%. |
| • | IAC command is greater than 145 counts. |
Action Taken When the DTC Sets
| • | The malfunction indicator lamp (MIL) will illuminate. |
| • | The PCM will record the operating conditions at the time that the diagnostic fails. The Freeze Frame and Failure Records buffers will store this information. |
| • | A history DTC stores. |
Conditions for Clearing the MIL/DTC
| • | The malfunction indicator lamp (MIL) will turn OFF after 3 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 a scan tool to clear the DTCs. |
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
Number(s) below refer to the step number(s) on the Diagnostic Table.
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The Powertrain OBD System Check prompts the technician to complete some basic checks and store the freeze frame and failure records data on the scan tool if applicable. This creates an electronic copy of the data taken when the malfunction occurred. The information is then stored on the scan tool 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. 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. This can be checked by checking the IAC valves internal resistance.
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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 so the test light should blink on all circuits when connected to ground.
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Any circuitry, that is suspected as causing the intermittent complaint, should be thoroughly checked for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wiring connections or physical damage to the wiring harness.
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A test light that remains ON constantly indicates that the circuit is shorted to voltage.
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Replacement PCMs must be reprogrammed and the crankshaft position system variation procedure must be performed. Refer to the latest Isuzu Technical Communication System (ITCS) information for programming procedures and also refer to the Powertrain Control Module (PCM) .
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If no malfunctions have been found at this point and no additional DTCs were set, refer to Diagnostic Aids for additional checks and information.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | Go to | ||
Does the engine RPM change smoothly when commanded by the scan tool? | 900-2000 RPM | |||
Are the resistance across terminals B and C and terminals A and D within the specified value? | 40-80ohms | |||
4 |
Are the resistance's across terminals B and C and terminals A and D infinite? | -- | ||
Does the test light illuminate on 2 terminals? | -- | |||
Connect a test light to B+ and probe the IAC electrical connector terminals. Does the test light illuminate on 2 terminals? | -- | |||
7 | Check for an open or short to ground in the IAC valve high and low circuits and repair as necessary. Was a repair necessary? | -- | ||
Does the test light flash ON and OFF for all terminals? | -- | |||
9 | Check for an open or a short to voltage in the IAC valve high and low circuits and repair as necessary. Was a repair necessary? | -- | ||
Check the PCM electrical connector for poor connections and repair as necessary. Was a repair necessary? | -- | |||
11 | Inspect the IAC valve passages. Was a problem found? | -- | ||
Did the test light remain ON constantly foe the terminals that did not blink? | -- | |||
13 | Check for a poor connection. If OK, replace the IAC valve. Refer to Idle Air Control Valve Replacement . Is the action complete? | -- | -- | |
Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Is the action complete? | -- | -- | ||
15 |
Does the scan tool indicate that this diagnostic has ran and passed? | -- | ||
Check if any additional DTCs are set. Are any DTCs displayed that have not been diagnosed? | -- | Go to applicable DTC table | System OK Refer to Diagnostic Aids |
