DTC P1508 - IAC SYSTEM LOW RPM GMC Envoy I

Note. For circuit reference, see WIRING DIAGRAMS - 4.3L article.

Circuit Description

VCM controls idle speed with an Idle Air Control (IAC) valve to a calculated RPM based on sensor inputs and actual engine RPM. VCM moves IAC valve in or out to vary amount of airflow into intake manifold and thus decrease or increase idle RPM.

VCM commands IAC in counts. A higher count, allows more air to by-pass throttle plate (higher idle).

Conditions for setting DTC

1. No ECT, MAP, TP or VSS sensor DTCs set.
2. ECT greater than 122°F (50°C).
3. IAT greater than -13°F (-25°C).
4. BARO greater than 70 kPa (10,300 ft.).
5. Vehicle speed less than 2 MPH.
6. System voltage 10-16 volts.
7. Throttle at idle or less than one percent.
8. Engine running longer than 30 seconds.
9. Conditions met for greater than 3 seconds.
10. Change in calculated airflow greater than 2 counts.