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 applies current to the IAC coils in pulses, or counts, to extend the IAC pintle into a passage in the throttle body in order to decrease the air flow. The PCM reverses the current in order to retract the pintle and increase the air flow. This method allows highly accurate control of the idle speed and quick response to changes in the engine load. If the PCM detects a condition where the idle speed is too low 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
| • | No active throttle position (TP), engine coolant temperature (ECT) , manifold absolute pressure (MAP), intake air temperature (IAT), mass air flow (MAF) , crankshaft position (CKP) , sensor, evaporative emissions (EVAP) , misfire, exhaust gas recirculation (EGR) , vehicle sensor speed (VSS), fuel trim (FT) or injector circuit DTCs are active. |
| • | The engine coolant temperature is more than 70°C (158°F). |
| • | The engine has been running for at least 2 minutes. |
| • | The system voltage is between 9.0--18.0 volts. |
| • | The vehicle speed is less than 3 mph. |
| • | The IAT is more than -18°C (5°F). |
| • | The throttle is below 1.5 percent. |
| • | The barometric pressure (BARO) is more than 65 kPa. |
Conditions for Setting the DTC
| • | The engine speed is more than 100 RPM less than Desired Idle. |
| • | The above condition exists for more than 15 seconds. |
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:
| • | A restricted air intake system--Inspect for: |
| - | A possible collapsed air intake duct |
| - | A restricted air filter element |
| - | Foreign objects that block the air intake system |
| • | The throttle body--Inspect for: |
| - | Objects that block the IAC passage or the throttle bore |
| - | Excessive deposits in the IAC passage and on the IAC pintle |
| - | Excessive deposits in the throttle bore and on the throttle plate |
| • | A large vacuum leak-- Inspect for a condition that causes a large vacuum leak, such as a incorrectly installed or faulty positive crankcase ventilation (PCV) valve or a brake booster hose that is disconnected. Refer to Visual and Physical Inspection in Symptoms . |
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 number below refers to the step number 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 other DTC first | |||||||||
3 |
Does engine speed remain within the specified value of the desired idle for each RPM command? | ±50 RPM | Go to Diagnostic Aids. | |||||||||
4 |
Does each node light cycle red and green, but never OFF? | -- | ||||||||||
5 |
Did you find and correct the condition? | -- | ||||||||||
6 | Inspect for a 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 | Inspect for the following conditions:
Do any of the above require a repair? | -- | ||||||||||
8 | Replace IAC valve. Refer to IAC Valve Replacement . Did you complete the replacement? | -- | -- | |||||||||
9 | Inspect for a faulty connection at the PCM harness connector. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems. Did you find and correct the condition? | -- | ||||||||||
|
Important: : Replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Did you complete the replacement? | -- | -- | ||||||||||
11 |
Does engine speed remain within the specified value of Desired Idle for each RPM command? | ±50 RPM | System OK |
