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.
1991 GMC Forward Control 6.2 J, AutomaticFACTORY OEM SERVICE PROCEDURE
Control Units
CONTROL UNITS LOCATION
| Component | Location | |
|---|---|---|
| ABS Control Module | On left side of engine compartment. | |
| Audio Alarm Module | Behind dash, below fuse block. | |
| Cruise Control Module | Behind instrument panel, near steering column. | |
| Digital Ratio Adaptor Controller (DRAC) | On parking brake lever assembly. | |
| Electronic Control Module (ECM) | ||
| 4.3L VIN Z | Under driver's seat. See Figure. | |
| 5.0L VIN H & 5.7L VIN K | Under driver's seat. See Figure. | |
| 7.4L VIN N | Under driver's seat. See Figure. | |
| Elec. Spark Control (ESC) Module | ||
| 4.3L VIN Z | Under driver's seat. See Figure. | |
| 5.0L VIN H & 5.7L VIN K | Under driver's seat. See Figure. | |
| 7.4L VIN N | Under driver's seat. See Figure. | |
| Glow Plug Controller (Diesel) | ||
| Controls & Relays | On left rear of intake manifold. See Figure. | |
| 6.2L Diesel | On left rear of intake manifold. See Figure. | |
| Hot Fuel Module | ||
| 5.0L VIN H & 5.7L VIN K | Under driver's seat. See Figure. | |
| 7.4L VIN N | Under driver's seat. See Figure. | |
| Hydro-Boost Elec. Delay Module | Behind left side of instrument panel. | |
| Light Driver Module (Diesel) | Under right side of dash. | |
| Power Door Lock Delay Module | Behind dash, to right of steering column. | |
| Pulse Wiper Control Module | Taped to harness, at left side of steering column. | |
Factory Service Tools
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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.