P0506

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DTC P0506 Idle Control System RPM Lower Than Expected




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 stepper motor driven by two coils. The PCM applies current to the IAC coils in steps (counts) to extend the IAC pintle into a passage in the throttle body to decrease air flow. The PCM reverses the current to retract the pintle, increasing air flow. 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. DTC P0506 is a type B code.

Conditions for Setting the DTC
- No intrusive tests being run.
- Engine run time is more than 125 seconds.
- No TPS, VSS, ECT, EGR, MAP, IAT, misfire, low voltage, fuel system or canister purge Diagnostic Trouble Codes are set.
- Barometric pressure is greater than 72.7 kPa.
- Canister purge duty cycle is above 0 %.
- Engine coolant temperature (ECT) is above 50 °C (122 °F).
- Intake air temperature above -40 °C (-40 °F).
- MAP is less than 60 kPa.
- Ignition voltage is between 9.5 volts and 16 volts.
- The throttle is closed.
- All conditions are met for 10 seconds.
- Engine speed is at least 100 RPM lower than desired idle, based upon PCM expectations.

Action Taken When the DTC Sets
- The PCM will illuminate the malfunction indicator lamp (MIL) after the second consecutive trip in which the fault is detected.
- The PCM will store conditions which were present when the Diagnostic Trouble Code was set as Freeze Frame and in the Failure Records data.

Conditions for Clearing the MIL/DTC
- Diagnostic Trouble Code P0506 can be cleared by using the Scan Tool's "Clear Info" function.

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; shorts to ground, shorts to battery positive, and open circuits.
- Restricted air intake system - Check for a possible collapsed air intake duct, restricted air filter element, or foreign objects blocking the air intake 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 an incorrectly installed or faulty PCV 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 that caused the Diagnostic Trouble Code to be set occurs. This may assist in diagnosing the condition.