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 MANUALSCHEVROLET2006SUBURBAN K2500, 6.0 UREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 1417 (ENGINE COOLING SYSTEM)DIAGNOSTIC INFORMATION AND PROCEDURESDTC P1258CIRCUIT/SYSTEM TESTING
2006 Chevrolet Suburban K2500, 6.0 U
Circuit/System Testing
2006 Chevrolet Suburban K2500, 6.0 USECTION Circuit/System Testing
WARNING: This page is about a different car, the 2009 GMC Sierra, 2009 GMC Cab & Chassis Sierra, 2009 Chevrolet Silverado, and 2009 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
- 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 Water Pump Replacement (LU3) or Water Pump Replacement (LMM) or Water Pump Replacement (LH6, LY2, LY5, and LMG) or Water Pump Replacement (LY6, L76, and L92) or Water Pump Replacement (LFA) .
- Inspect the engine for worn/leaking/cracked cylinder heads and engine block. Refer to Coolant in Combustion Chamber and Coolant in Engine Oil .
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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.