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 MANUALSGMC1999FORWARD CONTROL 5.7 R, AUTOMATICREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 631 (ENGINE COOLING SYSTEM)
1999 GMC Forward Control 5.7 R, Automatic
Section 631 (Engine Cooling System)
1999 GMC Forward Control 5.7 R, AutomaticSECTION Section 631 (Engine Cooling System)
WARNING: This page is about a different car, the 2003 Chevrolet Corvette. However, it is still accessible from the selected car via links, so may be relevant.
- Specifications
- Schematic and Routing Diagrams
- Component Locator
- Diagnostic Information and Procedures
- Diagnostic Starting Point - Engine Cooling
- Diagnostic System Check - Engine Cooling
- Scan Tool Data List
- Scan Tool Data Definitions
- DTC P0480: Improper Voltage Level On Low Speed Cooling Fan Relay Control Circuit
- DTC P0481: Improper Voltage Level On High Speed Cooling Fan Relay Control Circuit
- DTC P1258: Engine Over Temperature Condition
- Symptoms - Engine Cooling
- Thermostat Diagnosis
- Pressure Cap Testing
- Coolant Leak Testing
- Repair Instructions
- Draining and Filling Cooling System
- Flushing
- Surge Tank Replacement
- Radiator Hose Replacement - Inlet
- Radiator Hose Replacement - Outlet
- Throttle Body Heater Hose Replacement - Outlet
- Cooling Fan Replacement - Electric
- Cooling Fan Motor Replacement - Electric
- Cooling Fan Relay Replacement
- Thermostat Replacement
- Coolant Air Bleed Pipe Assembly Replacement
- Coolant Air Bleed Hose Replacement
- Water Pump Replacement
- Drain Cock Replacement
- Fan Shroud Replacement
- Radiator Replacement
- Radiator Support Replacement
- Radiator Air Baffle Assemblies and Deflectors
- Coolant Heater Replacement
- Coolant Heater Cord Replacement
- Description and Operation
- Special Tools and Equipment
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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.