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
| • | No active TP, ECT, MAP, IAT, MAF, CKP, sensor, EVAP, misfire, EGR, VSS, fuel trim, or injector circuit DTCs active. |
| • | Engine coolant temperature is above 70°C (158°F). |
| • | The engine has been running for at least 2 minutes. |
| • | System voltage is between 9.0-18.0 volts. |
| • | Vehicle speed is less than 3 mph. |
| • | Intake air temperature is above -18°C (5°F). |
| • | The throttle is below 1.5 percent. |
| • | BARO above 65 kPa. |
| • | Engine run time is more than 2 minutes. |
Conditions for Setting the DTC
| • | The IAC valve reads less than 15 counts on the scan tool. |
| • | Engine speed is more than 100 RPM higher than desired idle. |
Action Taken When the DTC Sets
| • | The PCM will illuminate the malfunction indicator lamp (MIL) during the second consecutive trip in which the diagnostic test has been run and failed. |
| • | The PCM will store conditions which were present when the DTC set as Freeze Frame/Failure Records data. |
Conditions for Clearing the MIL/DTC
| • | The PCM will turn OFF the malfunction indicator lamp (MIL) during the third consecutive trip in which the diagnostic has run and passed. |
| • | The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction. |
| • | The DTC can be cleared by using a scan tool. |
Diagnostic Aids
Inspect for the following conditions:
| • | Restricted air intake system--Inspect for a possible collapsed air intake duct, restricted air filter element, or foreign objects blocking the air intake system. |
| • | Throttle body--Inspect for objects blocking the IAC passage or throttle bore, excessive deposits in the IAC passage and on the IAC pintle, and excessive deposits in the throttle bore and on the throttle plate. |
| • | Large vacuum leak--Inspect for a condition that causes a large vacuum leak, such as a incorrectly installed or faulty PCV valve or brake booster hose disconnected. |
Many situations may lead to an intermittent condition. Perform each inspection or test as directed.
Important: : Remove any debris from the connector surfaces before servicing a component. Inspect the connector gaskets when diagnosing or replacing a component. Ensure that the gaskets are installed correctly. The gaskets prevent contaminate intrusion.
| • | Loose terminal connection |
| - | Use a corresponding mating terminal to test for proper tension. Refer to Testing for Intermittent Conditions and Poor Connections , and to Connector Repairs in Wiring Systems for diagnosis and repair. |
| - | Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and faulty terminal to wire connection. Refer to Testing for Intermittent Conditions and Poor Connections , and to Connector Repairs in Wiring Systems for diagnosis and repair. |
| • | Damaged harness--Inspect the wiring harness for damage. If the harness inspection does not reveal a problem, observe the display on the scan tool while moving connectors and wiring harnesses related to the sensor. A change in the scan tool display may indicate the location of the fault. Refer to Wiring Repairs in Wiring Systems for diagnosis and repair. |
| • | Inspect the powertrain control module (PCM) and the engine grounds for clean and secure connections. Refer to Wiring Repairs in Wiring Systems for diagnosis and repair. |
If the condition is determined to be intermittent, reviewing the Snapshot or Freeze Frame/Failure Records may be useful in determining when the DTC or condition was identified.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
Step | Action | Values | Yes | No | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||||||||||
2 | Are any other DTCs set? | -- | Go to applicable DTC | |||||||||
3 |
Does engine speed remain within the specified value of desired idle for each RPM commanded | 50 RPM | Go to Diagnostic Aids | |||||||||
4 |
Does the node light cycle from red to green (never OFF)? | -- | ||||||||||
5 |
Did you find and correct the condition? | -- | ||||||||||
6 | Inspect for faulty connection at the IAC harness connector. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems. Did you find and correct the condition? | -- | ||||||||||
7 |
| -- | ||||||||||
8 | Replace the IAC valve. Refer to Idle Air Control Valve Replacement . Did you complete the replacement? | -- | -- | |||||||||
9 |
Did you find and correct the condition? | -- | ||||||||||
|
Important: : Replacement PCM must be programmed. Refer to Powertrain Control Module Replacement/Programming . Replace the PCM. Did you complete the replacement? | -- | -- | ||||||||||
11 |
Does the engine speed remain within the specified value of desired idle for each RPM commanded | 50 RPM | System OK |
