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 MANUALSCHEVROLET1994SUBURBAN C2500, 7.4 NREPAIR AND DIAGNOSISTRANSMISSIONAUTOMATIC TRANSAUTOMATIC TRANSMISSION - DIAGNOSIS - 4L80-E
1994 Chevrolet Suburban C2500, 7.4 N
Automatic Transmission - Diagnosis - 4L80-E
1994 Chevrolet Suburban C2500, 7.4 NSECTION Automatic Transmission - Diagnosis - 4L80-E
- Application
- Description
- Operation
- Trouble Shooting
- Electronic Self-Diagnostics
- Diagnostic Charts
- Notes
- Chart A-1, No Mil (Service Engine Soon) Light
- Chart A-2, No ALDL Data, No DTC 12 Or Mil (Service Engine Soon) Light On
- DTC 14, Coolant Temperature Sensor High Temperature Indicated (Signal Voltage Low)
- DTC 15, Coolant Temperature Sensor Low Temperature Indicated (Signal Voltage High)
- DTC 21, Throttle Position Sensor Signal Voltage High
- DTC 21/22, Throttle Position Sensor Signal Voltage Low/High (1994) Diesel
- DTC 22, Throttle Position Sensor Signal Voltage Low
- DTC 24, Output Speed Sensor Low (1993 2WD)
- DTC 24, Output Speed Sensor Low (1993 4WD)
- DTC 24 & DTC 72, Vehicle Speed Sensor (Output Speed Signal Low) & (Output Speed Signal Loss) 1994
- DTC 28, Pressure Switch Manifold (PSM) Assembly Fault (1993)
- DTC 28, Pressure Switch Manifold (PSM) Assembly Fault (1994)
- DTC 37 & 38, TCC Brake Switch Stuck On Or Off (1994)
- DTC 39, Torque Converter Clutch Stuck Off (1993)
- DTC 39, Torque Converter Clutch Stuck Off (1994)
- DTC 51, Prom Problem
- DTC 52 & 53, Long System Voltage High Or System Voltage High (1994)
- DTC 53, System Voltage High (1993)
- DTC 58, Transmission Fluid Temperature Sensor Circuit (High Temperature Indicated) 1993
- DTC 58, Transmission Fluid Temperature Sensor Circuit (High Temperature Indicated) 1994
- DTC 59, Transmission Fluid Temperature Sensor Circuit (Low Temperature Indicated) 1993
- DTC 59, Transmission Fluid Temperature Sensor Circuit (Low Temperature Indicated) 1994
- DTC 63 & 64, Barometric Pressure Sensor Circuit High Or Low (1994) Diesel
- DTC 68, Overdrive Ratio Error (1993)
- DTC 68, Overdrive Ratio Error (1994)
- DTC 69, Torque Converter Clutch (TCC) Stuck On (1994)
- DTC 71, Camshaft Position Sensor Circuit Low (1994) Diesel
- DTC 73, Force Motor Current (Current Error) 1993
- DTC 73, Force Motor Current (Current Error) 1994
- DTC 74, Input Speed Sensor Circuit (1994)
- DTC 75, System Voltage Low (1993)
- DTC 75, System Voltage Low (1994)
- DTC 79, Transmission Fluid Temperature Sensor Circuit (High Temperature Indicated) 1994
- DTC 81, Solenoid "B" Circuit Fault (1993)
- DTC 81, Solenoid "B" Circuit Fault (1994)
- DTC 82, Solenoid "A" Circuit Fault (1993)
- DTC 82, Solenoid "A" Circuit Fault (1994)
- DTC 83, TCC Solenoid Circuit Fault (1993)
- DTC 83, TCC Solenoid Circuit Fault (1994)
- DTC 85, Undefined Gear Ratio (1993)
- DTC 85, Undefined Gear Ratio (1994)
- DTC 86, Low Gear Ratio (1993)
- DTC 86, Low Gear Ratio (1994)
- DTC 87, High Gear Ratio (1993)
- DTC 87, High Gear Ratio (1994)
- Component Test Charts (No Codes)
- Notes
- TCC Testing
- Vehicle Speed Sensor Check
- Input Speed Sensor Circuit (1993)
- Brake Signal Circuit (1993)
- Pressure Switch Manifold Circuit Check (1993-94)
- Torque Converter Clutch (TCC) Circuit Check (1993)
- Shift Solenoid "A" Circuit Check (1993)
- Shift Solenoid "B" Circuit Check (1993)
- Force Motor Circuit Check (1993)
- 4WD Low Switch Signal Check (1994)
- Wiring Diagrams
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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.