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.
1999 GMC Forward Control 4.3 W, StandardFACTORY OEM SERVICE PROCEDURE
Control Units
CONTROL UNITS
| Component | Component Location |
|---|---|
| Accelerator Pedal Position (APP) Module (Commercial Van) | Attached to accelerator pedal. |
| Accelerator Pedal Position (APP) Module (Motor Home) | Attached to accelerator pedal. See Figure. |
| Cruise Control Module | On radiator support bracket. |
| Daytime Running Lamps (DRL) Module | Attached to I/P harness (body builder installed). |
| Electronic Brake Control Module (EBCM) | Below radiator, on lower crossmember. |
| Fuel Balance Pump Module (Dual Tanks Only) | On inside of left frame rail. |
| Fuel Pump Module | On top center of fuel tank. |
| Fuel Solenoid Driver (6.5L VIN F) | On side of fuel injection pump. See Figure. |
| 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. |
| Ignition Control Module (ICM) (4.3L VIN W) | On right top of engine, at ignition coil. See Figure. |
| Ignition Control Module (ICM) (5.7L VIN R) | On right top of engine, at ignition coil. |
| Ignition Control Module (ICM) (7.4L VIN J) | On bracket at rear of intake plenum. See Figure. |
| Power Brake Booster Fluid Flow Indicator/Alarm Delay Module | Body builder installed. |
| Powertrain Control Module (PCM) (6.5L VIN F) | On left side of driver's island, on relay bracket. |
| Powertrain Control Module (PCM) (6.5L VIN Y) | On left side of driver's island, on relay bracket. |
| Seat Belt & Lamps Alarm Module | Attached to I/P fuse block. |
| Transmission Control Module (TCM) (6.5L VIN F) | On left side of driver's island, on relay bracket. |
| Transmission Control Module (TCM) (6.5L VIN Y) | On left side of driver's island, on relay bracket. |
| Vehicle Control Module (VCM) (Commercial Van) | On left side of radiator support. See Figure. |
| Vehicle Control Module (VCM) (Motor Home) | On top of radiator support. |
| Vehicle Speed Sensor (VSS) Calibrator (Motor Home) | On left side of driver's island, under relay bracket. 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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