P0506

Diagnostic Chart:

Wiring Diagram:

CIRCUIT DESCRIPTION

The VCM controls the idle speed with an Idle Air Control (IAC) valve to a calculated desired RPM based on the sensor inputs and the actual engine RPM. The VCM uses 4 circuits in order to move an Idle Air Control (IAC) valve, allowing a varying amount of air flow into the intake manifold.

In order to increase the idle RPM, the VCM moves the IAC valve out, allowing more air to bypass the throttle plate. In order to decrease the RPM, the VCM moves the IAC valve in, reducing the amount of air bypassing the throttle plate. A scan tool reads the VCM commands to the IAC valve in counts. The higher the counts, the more air is allowed to bypass the throttle plate (higher idle). The lower the counts, the less air that is allowed to bypass the throttle plates (lower idle).


CONDITIONS FOR SETTING DTC

Non-intrusive

^ No TP Sensor DTCs set

^ No ECT DTCs set

^ No VSS DTCs set

^ No MAP DTCs set

^ No transmission DTCs

^ No PRNDL DTCs

^ No Misfire DTCs

^ No IAT DTCs

^ No MAF DTCs

^ ECT is greater than 50°C

^ IAT is greater than -25°C

^ BARO is greater than 75 kPa

^ Vehicle Speed is less than 2 mph

^ System voltage is between 10 volts and 16 volts

^ Engine run time is greater than 30 seconds.

^ TP is less than 1%

^ Above met for a time greater than 3 seconds If the non-intrusive test fails, the intrusive test is run.

Intrusive

^ Air Flow is greater than 17.5 grams per second but less than 50 grams per second

^ Vehicle Speed is greater than 25 MPH but less than 85 MPH

^ Change in TP Sensor is less than 1%

^ Change in engine speed is less than 50 RPM

^ IAC motor is commanded to 10% for 100 msec


ACTION TAKEN WHEN THE DTC SETS

The VCM will turn ON the MIL after 2 consecutive driving cycles with the fault active.


CONDITIONS FOR CLEARING THE MIL/DTC

^ The VCM turns the MIL OFF after 3 consecutive drive trips when the test has Run and Passed and not Failed.

^ A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles (coolant temperature has risen 22°C (40°F) from the startup coolant temperature and the engine coolant temperature exceeds 70°C (160°F) during the same ignition cycle).

^ Use the scan tool Clear Information function.

^ Disconnect the VCM battery feed for 30 seconds.

DIAGNOSTIC AIDS

The following items could cause this DTC:

^ An IAC valve which is stopped and cannot respond to the VCM

^ A throttle stop screw which has been tampered with

^ A damaged throttle or linkage

A slow, unstable, or fast idle may be caused by a non IAC valve system problem that can not be overcome by the IAC valve. Out of range control IAC scan tool counts will read above 60 if the idle is too low and zero if the idle is too high. Check for the following:

^ Fuel system too lean and rich

^ Throttle body - inspect the bore for foreign material.

^ Refer to Rough, Unstable, or Incorrect Idle, Stalling. Rough, Unstable, or Incorrect Idle, Stalling

^ IAC reset is done with the scan tool misc. functions mode.