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 MANUALSCHEVROLET2003TRAILBLAZER 4.2 S, 4WDREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 1896 (ENGINE COOLING SYSTEM)DIAGNOSTIC INFORMATION AND PROCEDURESDTC P1258CIRCUIT/SYSTEM VERIFICATION
2003 Chevrolet TrailBlazer 4.2 S, 4WD
Circuit/System Verification
2003 Chevrolet TrailBlazer 4.2 S, 4WDSECTION Circuit/System Verification
WARNING: This page is about a different car, the 2009 Saturn Vue. However, it is still accessible from the selected car via links, so may be relevant.
NOTE:
If DTCs P0480, P0481, P0691, P0692, P0693, or P0694 are set, diagnose those DTCs first.
- Observe the engine coolant level. The engine coolant level should be within operating range. Refer to Capacities - Approximate Fluid, and Engine Coolant in the Owner's Manual.
- Ensure that the vehicle has the correct engine coolant, with correct concentration, and is not old, contaminated or contains additives. Refer to Recommended Fluids and Lubricants in the Owner's Manual.
- Inspect the cooling system for the following:
- Cooling system leaks
- Kinked or pinched hoses, especially at the radiator
- Loose, missing, or damaged radiator air seals or deflectors
- The radiator and A/C condenser for any air flow obstructions or bent fins-Refer to Symptoms - Engine Cooling .
- Command the cooling fans ON, in both low and high speed, if equipped.
- If the cooling fans do not operate as commanded, refer to Cooling Fan Inoperative (LAT) or Cooling Fan Inoperative (LE5) or Cooling Fan Inoperative (LCS) .
- Test the thermostat for correct operation. Refer to Thermostat Diagnosis .
- Test the engine cooling system for overheating. Refer to Engine Overheating .
- Inspect the water pump and coolant flow for correct operation. Refer to the following list:
- Water Pump Removal and Water Pump Cleaning and Inspection for LZ4
- Water Pump Removal and Water Pump Cleaning and Inspection for LP1, LY7 and LCS
- Inspect the engine mechanical for worn/leaking/cracked cylinder heads and engine block. Refer to the following list:
- Coolant in Combustion Chamber for LZ4
- Coolant in Combustion Chamber for LP1, LY7, and LCS
- Coolant in Engine Oil for LZ4
- Coolant in Engine Oil for LP1, LY7, and LCS
NOTE:
A small delay occurs before the ECM changes the cooling fan speed.
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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.