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 MANUALSCHEVROLET1987HI-CUBE 6.2 J, 400/M40REPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 24 (ENGINE CONTROLS - TESTS W/CODES - 6.5L DIESEL)SELF-DIAGNOSTIC SYSTEMDIAGNOSTIC PROCEDUREDIAGNOSTIC PROCEDURE
1987 Chevrolet Hi-Cube 6.2 J, 400/M40
Diagnostic Procedure
1987 Chevrolet Hi-Cube 6.2 J, 400/M40SECTION Diagnostic Procedure
WARNING: This page does not describe the selected car, but rather 10 other vehicles, including the 1994 GMC Yukon, 1994 GMC Suburban, 1994 GMC Pickup, 1994 GMC Cab & Chassis, and 1994 GMC C3500 HD. However, it is still accessible from the selected car via links, so may be relevant.
- Ensure all engine systems NOT related to the Diesel Electronic Control (DEC) system are operating properly. DO NOT proceed with testing unless all non-DEC system problems are repaired.
- ALWAYS begin diagnosis with diagnostic system check to determine if DEC system and PCM are working properly. See DIAGNOSTIC SYSTEM CHECK chart. If trouble codes, other than Diagnostic Trouble Code (DTC) 12 are displayed, determine if they are hard or intermittent trouble codes.
- A hard code is present while working on vehicle, and problem condition persists. Hard codes will cause Malfunction Indicator Light (MIL) to come on.NOTE: SERVICE ENGINE SOON light, located on instrument cluster, is also referred to as the Malfunction Indicator Light (MIL).
- An intermittent code does not reset itself and is NOT present while working on vehicle. Intermittent codes are often caused by loose connections. MIL will go out 10 seconds after fault goes away. For intermittent diagnostic procedures, proceed to the TESTS W/O CODES - 6.5L DIESEL article in this section.
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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.