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 MANUALSCHEVROLET1990CHEVY VAN G20, 5.0 H, 475/M40REPAIR AND DIAGNOSIS (SINGLE PAGE)TRANSMISSIONAUTOMATIC TRANSOVERHAUL & TESTING - 700-R4/4L60SERVICE BULLETINSPOSSIBLE BLOWN FUSES ON CIRCUITS 420, 422 OR 446 DUE TO SHORTED TCC WIRINGDIAGNOSTIC HINTS
1990 Chevrolet Chevy Van G20, 5.0 H, 475/M40
Diagnostic Hints
1990 Chevrolet Chevy Van G20, 5.0 H, 475/M40SECTION Diagnostic Hints
- If wire "A" (circuit 420) shorts to ground, check for blown fuse in 12-volt feed circuit. See TCC BATTERY FEED CIRCUIT
.NOTE: TCC BATTERY FEED CIRCUIT does not include all possible fuses. Check vehicle wiring diagram.TCC BATTERY FEED CIRCUIT
Vehicle Type & Body Code Check For Blown Fuse (Circuit 420) Passenger Cars B Gauges D G.A. Trans F Gauges Y Gauges Light Trucks & Vans C/K ECM/Ignition M Gauges R/V Gauges/Idle G Gauges S/T Ignition/Gauges - If wire "D" (circuit 422) shorts to ground, 3 different conditions may occur:
- TCC may engage if transmission is too hot and there is short in White wire between TCC and TCC switch.
- Engine may idle rough. If transmission has 4th gear switch and there is short between ECM and switch, ECM always receives signal that transmission is in 4th gear. This may affect engine performance if spark timing depends on gear position.
- If wire "B" (circuit 446) shorts to ground, TCC will engage after a 1-2 shift (all except S and T truck with 2.5L engine).
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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.