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.
1985 GMC Forward Control 6.2 J, StandardFACTORY OEM SERVICE PROCEDURE
Diesel CEC Tests W/Codes
Select a section or procedure below to view factory instructions:
DescriptionBasic Diagnostic ProcedureReading Trouble CodesTrouble Code IdentificationClearing Trouble CodesDiagnostic Circuit CheckDDC Tester CheckECM Check CEL Doesn't Flash Code 12 Or Remains OnEPR Solenoid Electrical CheckEPR Vacuum CheckTCC CheckCold Advance Control CheckCode 12 - No Reference PulseCode 21 - TPS Open Or MISADJUSTEDCode 22 - TPS Grounded Or MISADJUSTEDCode 24 - Vehicle Speed SensorCode 31 - Map Sensor Voltage Too LowCode 32 - EGR Loop ErrorCode 33 - Map Sensor Voltage Too HighCode 51 - Faulty PromCode 52 - Faulty ECMCode 53 - Reference Voltage OverloadECM Terminal Identification & Pin Voltages
Factory Service Tools
Use the Manual With the Right Hardware
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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.