Circuit Description

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

To increase idle RPM, VCM moves IAC valve out, allowing more air to by-pass throttle plate. To decrease RPM, VCM moves IAC valve in, reducing amount of air by-passing throttle plate. Scan tool reads VCM commands to IAC valve in counts. The higher the counts, the more air that is allowed to by-pass throttle plate (higher idle). The lower the counts, less air is allowed to by-pass throttle plates (lower idle).

DTC will test when the following conditions are present:

• No TP sensor DTCs are set.
• No ECT sensor DTCs are set.
• ECT greater than 162°F (72°C).
• IAT greater than -13°F (-25°C).
• BARO is greater than 70 kPa (less than 10,300 ft.).
• Vehicle speed is less than 2 MPH.
• No VSS DTCs are set.
• No MAP sensor DTCs are set.
• System voltage greater than 10 volts but less than 18 volts.
• Engine run time is greater than 30 seconds.
• Throttle position is less than 1 percent.
• All conditions are met for greater than 3 seconds.