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.
2003 Hummer H2FACTORY OEM SERVICE PROCEDURE
Section 603 (Engine Cooling System)
WARNING: This page is about a different car, the 2004 Hummer H2. 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 Output Controls
- Scan Tool Data List
- Scan Tool Data Definitions
- Diagnostic Trouble Code (DTC) List
- DTC P1258
- Symptoms - Engine Cooling
- Engine Overheated Indicator Always On
- Engine Coolant Temperature Indicator Always On
- Low Engine Coolant Indicator Always On
- Engine Overheating
- Loss of Coolant
- Thermostat Diagnosis
- Coolant Heater Inoperative
- Engine Fails To Reach Normal Operating Temperature
- Pressure Cap Testing
- Coolant Leak Testing
- Fan Clutch Diagnosis
- Repair Instructions
- Draining and Filling Cooling System
- Flushing
- Radiator Cleaning
- Surge Tank Replacement
- Surge Tank Hose/Pipe Replacement - Inlet
- Surge Tank Hose/Pipe Replacement - Outlet
- Radiator Hose Replacement - Inlet
- Radiator Hose Replacement - Outlet
- Radiator Vent Inlet Hose Replacement
- Engine Oil Cooler Pipe/Hose Quick Connect Fitting
- Engine Oil Cooler Hose/Pipe Replacement
- Fan Replacement
- Fan Clutch Replacement
- Thermostat Housing Replacement
- Coolant Air Bleed Pipe Assembly Replacement
- Coolant Air Bleed Hose Replacement
- Water Pump Replacement
- Drain Cock Replacement
- Fan Shroud Replacement
- Radiator Replacement
- Radiator Air Baffle Assemblies and Deflectors
- Coolant Heater Replacement
- Coolant Heater Cord Replacement
- Description and Operation
- Special Tools and Equipment
Factory Service Tools
Use the Manual With the Right Hardware
Pair factory procedures with proven DIY tools so the instructions are easier to execute.
Disclosure: Verified tool recommendations may earn an affiliate commission at no cost to you.
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.