P0506

CIRCUIT DESCRIPTION
The VCM controls the idle speed with an Idle Air Control (IAC) valve to a calculated desired RPM based on sensor inputs and actual engine RPM. The VCM uses 4 circuits in order to move an Idle Air Control (IAC) valve, allowing a varying amounts 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 that 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). This DTC is a type B DTC.

CONDITIONS FOR SETTING THE DTC
The following conditions will set the DTC:

^ No TP sensor DTCs.
^ No ECT DTCs.
^ ECT greater than 72°C.
^ IAT greater than -25°C.
^ Baro greater than 70 kPa (less than 10,300 ft.).
^ Vehicle Speed Sensor (VSS) less than 2 mph.
^ No VSS DTCs.
^ No MAP DTCs.
^ System voltage greater than 10 volts but less than 18 volts.
^ Engine run time greater than 30 seconds.
^ TP less than 1%.
^ Above met for a time greater than 3 seconds in order to enable diagnostic.

ACTION TAKEN WHEN THE DTC SETS
The VCM turns on the Malfunction Indicator Lamp (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 driving trips without a fault condition present. A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles (coolant temperature has risen 40°F from the start-up coolant temperature and the engine coolant temperature exceeds 160°F during that same ignition cycle) or the scan tool clearing feature has been used.

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 cannot 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.
^ IAC reset is done with the scan tool misc. functions mode.