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 18 (ENGINE CONTROLS - TESTS W/CODES - 7.4L)SELF-DIAGNOSTIC SYSTEMDIAGNOSTIC 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 18 other vehicles, including the 1994 GMC Vandura Special, 1994 GMC Vandura, 1994 GMC Suburban, 1994 GMC Rally Camper Special, and 1994 GMC Rally. However, it is still accessible from the selected car via links, so may be relevant.
Diagnosis of the computerized engine control system should be performed in the following order:
- Ensure all engine systems not related to the computer are operating properly. DO NOT proceed with testing unless all other problems have been repaired. Perform diagnostic circuit check before using trouble code charts. See appropriate BASIC TESTING
article in the ENGINE PERFORMANCE section below.
- BASIC TESTING - GASOLINE (for "C" & "K" Series)
- BASIC TESTING - GASOLINE (For "G" & "P" Series)
- If trouble codes were displayed (other than Code 12), determine whether codes are hard or intermittent. Hard codes cause Malfunction Indicator Light (MIL) to illuminate continuously with engine running. See HARD OR INTERMITTENT TROUBLE CODE DETERMINATION. For diagnosing hard codes, proceed to appropriate trouble code chart. For diagnosing intermittent codes, proceed to INTERMITTENTS in appropriate TESTS W/O CODES article in the ENGINE PERFORMANCE section below. Exceptions are Code 13, 15, 24, 44 and 45 charts, which can help diagnose intermittent codes.
- If trouble codes were not displayed and a driveability problem exists, refer to SYMPTOMS in appropriate TESTS W/O CODES article in the ENGINE PERFORMANCE section above. From there you will be sent to the appropriate area in appropriate I - SYS/COMP TESTS article in the ENGINE PERFORMANCE section below.
- After repairs are made, clear trouble codes and perform FIELD SERVICE MODE CHECK in appropriate BASIC TESTING article in the ENGINE PERFORMANCE section below.
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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.