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 MANUALSCHEVROLET1993FORWARD CONTROL 7.4 NREPAIR AND DIAGNOSIS (SINGLE PAGE)ENGINE PERFORMANCESYSTEMENGINE CONTROLS - SYSTEM/COMPONENT TESTSMISCELLANEOUS ECM CONTROLSCHART C-12, COOLING FAN CIRCUIT DIAGNOSIS 3.1LOVERVIEW
1993 Chevrolet Forward Control 7.4 N
Chart C-12, Cooling Fan Circuit Diagnosis 3.1L: Overview
1993 Chevrolet Forward Control 7.4 NSECTION Overview
NOTE:
Test numbers refer to numbers on diagnostic charts.
- Battery voltage should be available at cooling fan relay terminals "A" and "D" when ignition switch is in ON position.
- This checks ECM's ability to ground circuits No. 335 and 473. Malfunction Indicator Light (MIL) should be flashing at this point. If MIL is not flashing, refer to TESTS W/CODES article in this section.
- This test checks if cooling puller and pusher fan relays (circuits No. 533 and 702) are open. Jumpering relay terminals "A" and "E" by-passes relay, which should cause fans to operate, if motors and wiring are okay.
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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.