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
- The IAC valve reads greater than 150 counts on the scan tool.
- The barometer is greater than 72 kPa.
- The ECT sensor indicates temperature greater than 40° C.
- The idle speed deviates below desired rpm by greater than 60 RPM for greater than 5 seconds.
- The engine run time is greater than 20 seconds.
- The battery voltage is between 10 and 17 volts.
- The TP angle is less than 1 %.
- One or more of the following DTCs are not set: P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0131, P0132, P0133, P0134, P0335, P0341, P0342, P0502, P0503, P0562, P0563, P0600, P1133, P1520.
Action Taken When the DTC Sets
| • | The Malfunction Indicator Lamp (MIL) illuminates after 2 consecutive ignition cycles in which the diagnostic runs with the fault active. |
| • | The PCM records the operating conditions at the time the diagnostic fails. The Freeze Frame and Failure Records buffers stores this information. |
| • | A history DTC is stored. |
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
The numbers below refer to the step numbers on the diagnostic table.
-
The Powertrain OBD System Check prompts the technician to complete some basic checks and store the Freeze Frame Data and the Failure Records on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurs. Refer to this information on the scan tool later.
-
Before replacing the PCM, check the terminals for improper mating, broken locks, or physical damage to the wiring harness. Reprogram the replacement PCM. Refer to the latest Techline information for programming procedures.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | |||
2 |
Does the RPM change smoothly when commanded by the scan tool? | 900 to 2000 RPM | ||
3 |
Are the resistances across terminals A and B and terminals C and D within the specified value? | 40 to 80 ohms | ||
4 |
Are the resistances across terminals B and C and terminals A and D infinite? | -- | ||
5 |
Does the test lamp illuminate on 2 terminals? | -- | ||
6 | With a test lamp connected to B+, probe the IAC electrical connector terminals. Does the test lamp illuminate on 2 terminals? | -- | ||
7 |
Was a repair necessary? | -- | ||
8 |
Does the test lamp flash ON and OFF for all the terminals? | -- | ||
9 |
Was a repair necessary? | -- | ||
10 |
Was a repair necessary? | -- | ||
11 |
Was a problem found? | -- | ||
12 | Did the test lamp remain ON constantly for the terminals that did not flash? | -- | ||
13 | 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 ran and passed? | 90°-95° C | ||
16 | Check if any additional DTCs are set. Are any DTCs displayed that have not been diagnosed? | -- | Go to the Applicable DTC Table | System OK |
