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 MANUALSCHEVROLET1991R 30 P/U 2WD V8-454 7.4LREPAIR AND DIAGNOSISRELAYS AND MODULESRELAYS AND MODULES - POWERTRAIN MANAGEMENTRELAYS AND MODULES - COMPUTERS AND CONTROL SYSTEMSENGINE CONTROL MODULETESTING AND INSPECTIONELECTRONIC CONTROL MODULE (ECM) TESTS - TBIMANUAL. TRANS. SHIFT LIGHT CHECK
1991 Chevrolet R 30 P/U 2WD V8-454 7.4L
Manual. Trans. Shift Light Check
1991 Chevrolet R 30 P/U 2WD V8-454 7.4LSECTION Manual. Trans. Shift Light Check
Chart C-8B - Manual Transmission Shift Light Check (Below 8500 GVW):
Wiring Diagram For Chart C-8B - Manual Transmission Shift Light Check (Below 8500 GVW):
MANUAL. TRANS. SHIFT LIGHT CHECK (BELOW 8500 GVW)
CIRCUIT DESCRIPTION:
The ECM uses information from the following inputs to control the shift light:
^ Coolant temperature
^ TPS
^ VSS
^ RPM
The ECM uses the measured rpm and the vehicle speed to calculate what gear the vehicle is in. It's this calculation that determines when the shift light should be turned on.
TEST DESCRIPTION: Numbers below refer to circled numbers on the diagnostic chart.
1. This should not turn "ON" the shift light. If the light "ON", there is a short to ground in CKT 456 wiring, or a fault in the ECM.
2. This should turn "ON" the shift light.
3. This checks for an open in the shift light circuit, or 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.