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).

Conditions for setting DTC:

• No ECT, MAP, TP or VS sensor DTCs are set.
• ECT greater than 122°F (50°C).
• IAT greater than -13°F (-25°C).
• BARO greater than 70 kPa (10,300 ft.).
• Vehicle speed less than 2 MPH.
• System voltage 10-16 volts.
• Engine run time greater than 30 seconds.
• TP less than one percent.
• Conditions are met for greater than 3 seconds.