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 MANUALSCHEVROLET1991SUBURBAN 1/2 TON 4WD V8-350 5.7LREPAIR AND DIAGNOSISPOWERTRAIN MANAGEMENTCOMPUTERS AND CONTROL SYSTEMSENGINE CONTROL MODULETESTING AND INSPECTIONELECTRONIC CONTROL MODULE (ECM) TESTS - TBICRANK SIGNAL DIAGNOSIS
1991 Chevrolet Suburban 1/2 Ton 4WD V8-350 5.7L
Crank Signal Diagnosis
1991 Chevrolet Suburban 1/2 Ton 4WD V8-350 5.7LSECTION Crank Signal Diagnosis
Chart C-1B - Crank Signal Diagnosis:
Wiring Diagram For Chart C-1B - Crank Signal Diagnosis:
CRANK SIGNAL DIAGNOSIS
CIRCUIT DESCRIPTION:
Crank signal is a 12 volts signal to the ECM during cranking to allow enrichment and cancel diagnostics until engine is running or 12 volts is no longer on circuit.
TEST DESCRIPTION: Numbers below refer to circled numbers on the diagnostic chart.
1. Checks for normal (cranking) voltage to terminal "C9" of ECM. Test light should be "ON" during cranking and then go "OFF" when engine is running.
2. Checks to determine if source of blown fuse or fuse link was a faulty ECM.
RENDER: 1.0x
NO RELATED
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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.