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.
1998 GMC Forward Control 6.5 FFACTORY OEM SERVICE PROCEDURE
Control Units
CONTROL UNITS
| Component | Component Location |
|---|---|
| Accelerator Pedal Position (APP) Module (6.5L VIN F) | Attached to accelerator pedal. See Figure. |
| Accelerator Pedal Position (APP) Module (6.5L VIN Y) | Attached to accelerator pedal. |
| Cruise Control Module | On radiator support bracket. |
| Daytime Running Lamps (DRL) Module | Behind dash, above steering column. |
| Electronic Brake Control Module (EBCM) | Below radiator, on first crossmember. |
| Electronic Ignition Coil Driver Module (4.3L VIN W) | On right top of engine. See Figure. |
| Electronic Ignition Coil Driver Module (5.7L VIN R) | On right top of engine. See Figure. |
| Electronic Ignition Coil Driver Module (7.4L VIN J) | On bracket at rear of intake plenum. See Figure. |
| Fuel Balance Pump Module (7.4L VIN J) (Dual Tanks Only) | On inside of left frame rail. |
| Glow Plug Controller (6.5L VIN F) | On left rear of engine, near firewall. |
| Glow Plug Controller (6.5L VIN Y) | On left rear of engine, near firewall. |
| P/B Booster Fluid Flow Indicator/ Alarm Delay Module (School Bus) | On brake warning system harness, taped to dash harness at breakout to dash fuse block & headlamps switch. |
| Powertrain Control Module (PCM) (6.5L VIN F) | On left side of driver's island. See Figure. |
| Powertrain Control Module (PCM) (6.5L VIN Y) | On left side of driver's island. |
| Transmission Control Module (TCM) (6.5L VIN F) | On left interior firewall, on top of relay bracket. |
| Transmission Control Module (TCM) (6.5L VIN Y) | On left interior firewall, on top of relay bracket. |
| Vehicle Control Module (VCM) (4.3L VIN W) | On left side of engine compartment. See Figure. |
| Vehicle Control Module (VCM) (5.7L VIN R) | On left side of engine compartment. See Figure. |
| Vehicle Control Module (VCM) (7.4L VIN J) | On center front of engine compartment. See Figure. |
| Windshield Wiper Pulse Control Module | Tie strapped to engine wiring harness, under driver's island support. |
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.
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