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 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, pintle 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.
Conditions for Running the DTC
| • | No VSS, TP Sensor, EVAP System, Misfire, IAT Sensor, MAP Sensor, Fuel Trim, Fuel Injector, EGR Pintle Position, ECT Sensor, CKP Sensor, or MAF Sensor DTCs set. |
| • | BARO is more than 65 kPa. |
| • | Engine has been running for at least 2 minutes. |
| • | System voltage is between 9-16 volts. |
| • | Engine coolant temperature is more than 70°C (158°F). |
| • | Vehicle speed is less than 3 mph. |
| • | Intake air temperature is more than -18°C (0°F). |
| • | The throttle is closed. |
Conditions for Setting the DTC
| • | Engine speed is more than 100 RPM lower than Desired Idle. Negative idle speed error is more than 100 RPM. |
| • | The above conditions are present for longer 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:
| • | 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 an incorrectly installed or malfunctioning crankcase ventilation 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 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? | -- | ||||||||||
3 |
Does Engine Speed vary less than the specified value from each RPM command? | 50 RPM | Go to Diagnostic Aids. | |||||||||
4 |
Does each node lamp cycle red and green, never off? | -- | ||||||||||
5 |
Did you find and correct the condition? | -- | ||||||||||
6 |
Did you find and correct the condition? | -- | ||||||||||
7 | Visually and physically inspect for the following conditions:
Did you find and correct any condition? | -- | ||||||||||
8 | Replace IAC valve. Refer to Idle Air Control Valve Replacement . Is the action complete? | -- | -- | |||||||||
9 |
Did you find and correct the condition? | -- | ||||||||||
|
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 vary less than the specified value from each RPM command? | 50 RPM | System OK |
