Circuit Description
The 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 (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 (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 indicating a problem with the idle control system.
Conditions for Running the DTC
| • | No VSS, TP sensor, EVAP system, Misfire, IAT sensor, Fuel Trim, Fuel Injector circuit, EGR Pintle, ECT sensor, CKP sensor, MAP sensor or MAF sensor DTC(s) are set. |
| • | Engine Coolant Temperature is greater than 50°C (122°F). |
| • | BARO is greater than 65 kPa. |
| • | The engine has been running for at least 2 minutes. |
| • | System voltage is between 9-16 volts. |
| • | Vehicle Speed is less than 3 mph. |
| • | Intake Air Temperature is greater than -18°C (0°F). |
Conditions for Setting the DTC
| • | The throttle is closed (below 1.5%) |
| • | Engine Speed is between 180 RPM - 200 RPM lower than Desired Idle. |
Action Taken When the DTC Sets
| • | The PCM will illuminate the 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 and Fail Records data. |
Conditions for Clearing the MIL/DTC
| • | The PCM will turn the MIL OFF during the third consecutive trip in which the diagnostic has been 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 the scan tool Clear Info function or by disconnecting the PCM battery feed. |
Diagnostic Aids
Check for the following conditions:
| • | Poor connection at PCM or IAC motor. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection. |
| • | Damaged harness. Inspect the wiring harness for damage. |
| • | Restricted air intake system. Check for a possible collapsed air intake duct, restricted air filter element, or foreign objects blocking the air intake system. Refer to Air Induction System . |
| • | 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. |
| • | Large vacuum leak. Check for a condition that causes a large vacuum leak, such as a incorrectly installed or faulty crankcase ventilation valve or brake booster hose disconnected. Refer to Emission Hose Routing Diagram . |
Reviewing the Fail Records vehicle mileage since the diagnostic test last failed may help determine how often the condition that caused the DTC to be set occurs. This may assist in diagnosing the condition.
Test Description
Number(s) below refer to the step number(s) on the Diagnostic Table.
Step | Action | Value(s) | Yes | No | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | Was the Powertrain On-Board Diagnostic System Check performed? | -- | Go to the A Powertrain On Board Diagnostic (OBD) System Check | |||||||||||
2 | Are any other DTC(s) set? | -- | Diagnose the other DTC(s) first. Refer to Powertrain Control Module Diagnosis (PCM Diagnostic Trouble Codes) . | |||||||||||
3 |
Does Engine Speed remain within the specified value of Desired Idle for each rpm command? | ±50 rpm | Refer to Diagnostic Aids | |||||||||||
4 |
Does each node light cycle red and green (never OFF)? | -- | ||||||||||||
5 |
Was a problem found? | -- | ||||||||||||
6 | Visually/physically inspect for the following conditions:
Does any of the above require a repair? | -- | Refer to appropriate section for on-vehicle service | |||||||||||
7 |
Was a problem found? | -- | ||||||||||||
8 | Replace IAC valve. Refer to IAC Valve Replacement . Is action complete? | -- | -- | |||||||||||
9 |
Was a problem found? | -- | ||||||||||||
Replace the PCM. Important: Replacement PCM must be programmed. Refer to PCM Replacement/Programming . Is action complete? | -- | -- | ||||||||||||
11 |
Does Engine Speed remain within the specified value of Desired Idle for each rpm command? | ±50 rpm | System OK |
