Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSGMC1992C3500 HD 6.5 F, STANDARDREPAIR AND DIAGNOSISENGINE PERFORMANCESYSTEMENGINE CONTROLS - SYSTEM/COMPONENT TESTSFUEL SYSTEM (GASOLINE)IDLE CONTROL SYSTEMIDLE AIR CONTROL (IAC) MOTOR
1992 GMC C3500 HD 6.5 F, Standard
Idle Air Control (IAC) Motor
1992 GMC C3500 HD 6.5 F, StandardSECTION Idle Air Control (IAC) Motor
- Disconnect harness connector to motor. Check resistance across IAC coil terminals "A" to "B" and "C" to "D". See Fig 1. Resistance should be 40-80 ohms. If okay, go to next step. If resistance is not as specified, replace IAC motor.
- Check resistance between IAC terminals "B" to "C" and "A" to "D". Resistance should be infinite. If resistance is not as specified, replace IAC motor
NOTE:
Functional testing of Idle Air Control (IAC) motor requires a scan tester capable of cycling ECM output devices (bidirectional) or a special IAC Driver and Node Light Set (222L or J-37027). Flow charts in the G - TESTS W/ CODES articles may refer to the Tech 1 tester, General Motors' bidirectional tester.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.