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 MANUALSGMC1994C3500 HD 6.5 F, AUTOMATICREPAIR AND DIAGNOSISENGINE PERFORMANCESYSTEMENGINE CONTROLS - TESTS W/CODES - 6.5L DIESEL
1994 GMC C3500 HD 6.5 F, Automatic
Engine Controls - Tests W/Codes - 6.5L Diesel
1994 GMC C3500 HD 6.5 F, AutomaticSECTION Engine Controls - Tests W/Codes - 6.5L Diesel
- Introduction
- Self-Diagnostic System
- TDC Offset Program Procedure
- Diagnostic Trouble Code (DTC) Identification
- Diagnostic Trouble Code Charts
- DTC 13 - Engine Shutoff Solenoid Circuit Fault
- DTC 14 - ECT Sensor Circuit Low (High Temperature Indicated)
- DTC 15 - ECT Sensor Circuit High (Low Temperature Indicated)
- DTC 16 - Vehicle Speed Signal Buffer Fault
- DTC 17 - High Resolution Circuit Fault
- DTC 18 - Pump Cam Reference Pulse Error
- DTC 19 - Crankshaft Position Reference Error
- DTC 21 - Accelerator Pedal Position (App) No. 1 Circuit High
- DTC 22 - Accelerator Pedal Position (App) No. 1 Circuit Low
- DTC 23 - Accelerator Pedal Pos (App) No. 1 CKT Range Fault
- DTC 25 - Accelerator Pedal Position (App) No. 2 Circuit High
- DTC 26 - Accelerator Pedal Position (App) No. 2 Circuit Low
- DTC 27 - Accelerator Pedal Pos (App) No. 2 CKT Range Fault
- DTC 29 - Glow Plug Relay Circuit Fault
- DTC 31 - EGR CNTRL Pressure/BARO Sensor CKT Low (High Vacuum)
- DTC 32 - EGR Circuit Error
- DTC 33 - EGR CNTRL Pressure/BARO Sensor CKT High (Low Vacuum)
- DTC 34 - Injection Timing Stepper (Its) Motor Circuit Fault
- DTC 35 - Injection Pulse Width Error (Response Time Short)
- DTC 36 - Injection Pulse Width Error (Response Time Long)
- DTC 41 - Brake Switch Circuit Fault
- DTC 42 - Fuel Temperature CKT Low (High Temp Indicated)
- DTC 43 - Fuel Temperature CKT High (Low Temp Indicated)
- DTC 44 - EGR Pulse Width Error
- DTC 45 - EGR Vent Error
- DTC 46 - Mil (Service Engine Soon Light) Circuit Fault
- DTC 47 - IAT Sensor Circuit Low (High Temperature Indicated)
- DTC 48 - IAT Sensor Circuit High (Low Temperature Indicated)
- DTC 49 - Mil (Service Throttle Soon Light) Circuit Fault
- DTC 51 - Prom Problem (Faulty Or Incorrect Prom)
- DTC 54 - Pcm Fuel Circuit Error
- DTC 56 - Injection Pump Calibration Resistor Error
- DTC 57 - Pcm 5-Volt Shorted
- DTC 61 - Turbo Boost Sensor CKT High
- DTC 62 - Turbo Boost Sensor CKT Low
- DTC 63 - Accelerator Pedal Position (App) No. 3 Circuit High
- DTC 64 - Accelerator Pedal Position (App) No. 3 Circuit Low
- DTC 65 - App No. 3 Circuit Range Fault
- DTC 71 - Set/Coast Switch Fault
- DTC 76 - Resume/ACCEL Switch Fault
- DTC 78 - WASTEGATE Solenoid Fault
- DTC 84 - Accelerator Pedal Position (App) Circuit Fault
- DTC 88 - TDC Offset Error
- DTC'S 91-98 - Cylinder Balance Fault
- DTC 99 - APP No. 2 (5-VOLT REFERENCE FAULT)
- Wiring Diagrams
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.