Refer to Engine Controls Schematics
MAF, Secondary Air Injection Pump Bypass Solenoid, IAC and Secondary
AIR Pump
.
Circuit Description
The powertrain control module (PCM) controls engine idle speed by adjusting the position of the idle air control (IAC) motor pintle. The IAC is a bi-directional motor driven by two coils. The PCM sends pulses, or steps, to the IAC to extend or retract the IAC pintle into a passage in the throttle body to decrease or increase air flow. The commanded IAC position, displayed in counts, can be monitored on the scan tool. A higher number of counts indicates more commanded airflow, and the pintle is retracted. This method allows highly accurate control of idle speed and quick response to changes in engine load. If the PCM detects a condition where too low of an idle speed is present and the PCM is unable to adjust idle speed by increasing the IAC counts, DTC P0506 will set indicating a problem with the idle control system.
Conditions for Running the DTC
| • | The following types of diagnostic trouble codes (DTCs) are not set: |
| • | Fuel injector faults |
| • | Misfire |
| • | Fuel trim |
| • | Evaporative emission (EVAP) system |
| • | Exhaust gas recirculation (EGR) system |
| • | Vehicle speed sensor (VSS) |
| • | Throttle position (TP) sensor |
| • | Intake air temperature (IAT) sensor |
| • | Manifold absolute pressure (MAP) sensor |
| • | Engine coolant temperature (ECT) sensor |
| • | Crankshaft position (CKP) sensor |
| • | Mass air flow (MAF) sensor |
| • | The BARO is more than 65 kPa. |
| • | The engine has been running for at least 3 minutes. |
| • | The system voltage is between 9-18 volts. |
| • | The engine coolant temperature is more than 70°C (158°F). |
| • | The vehicle speed is less than 3 mph. |
| • | The intake air temperature is more than -18°C (0°F). |
| • | The throttle is closed. |
| • | The conditions are stable for at least 15 seconds. |
Conditions for Setting the DTC
The engine speed is more than 100 RPM lower than the Desired Idle. The negative idle speed error is more than 100 RPM.
Action Taken When the DTC Sets
| • | The PCM illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails. |
| • | The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the conditions to the Freeze Frame and updates the Failure Records. |
Conditions for Clearing the MIL/DTC
| • | The PCM turns the MIL OFF after 3 consecutive drive trips during which the diagnostic runs and passes. |
| • | A last test failed, or the current DTC, clears when the diagnostic runs and passes. |
| • | A History DTC clears after 40 consecutive warm-up cycles, if no other emission related diagnostic failures are reported. |
| • | Use a scan tool in order to clear the MIL diagnostic trouble code. |
| • | Interrupting the PCM battery voltage may or may not clear DTCs. This practice is not recommended. Refer to Powertrain Control Module Description , Clearing Diagnostic Trouble Codes. |
Diagnostic Aids
Notice: Use the connector test adapter kit J 35616-A for any test that
requires probing the following items:
• The PCM harness connectors • The electrical center fuse/relay cavities • The component terminals • The component harness connector
Check for the following conditions:
| • | A poor connection at PCM or IAC motor -- Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection. |
| • | A damaged harness -- Inspect the wiring harness for damage. |
| • | A restricted air intake system -- Check for a possible collapsed air intake duct, restricted air filter element, or foreign objects blocking the air intake system. |
| • | The throttle body -- Check 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. |
| • | A large vacuum leak -- Check for a condition that causes a large vacuum leak, such as a incorrectly installed or malfunctioning crankcase ventilation valve or brake booster hose disconnected. |
Reviewing the Failure Records vehicle mileage since the diagnostic test last failed may help determine how often the condition occurs that caused the DTC to set . This may assist in diagnosing the condition.
If the problem is intermittent, refer to Intermittent Conditions .
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 the applicable DTC table | |||||||||
3 |
Does engine speed remain within the specified value of Desired Idle for each RPM command? | ± 100 RPM | Go to Diagnostic Aids | |||||||||
4 |
Does each node lamp cycle red and green, but never OFF? | -- | ||||||||||
5 |
Was a problem found and corrected? | -- | ||||||||||
6 |
Was a problem found and corrected? | -- | ||||||||||
7 |
Was a problem found and corrected? | -- | ||||||||||
8 | Replace the IAC valve. Refer to Idle Air Control Valve Replacement . Is the action complete? | -- | -- | |||||||||
9 |
Was a problem found and corrected? | -- | ||||||||||
|
Important: The replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Is the action complete? | -- | -- | ||||||||||
11 |
Does engine speed remain within the specified value of Desired Idle for each RPM command? | ± 100 RPM | ||||||||||
12 | Review Captured Info using the scan tool. Are there any DTCs that have not been diagnosed? | -- | Go to the applicable DTC table | System OK |
