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Home >> Cadillac >> 2007 >> Escalade EXT >> Repair and Diagnosis >> External Pages >> Different car >> Section 1023 (Engine Cooling System) >> Diagnostic Information and Procedures >> DTC P1258 >> Circuit/System Testing
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Circuit/System Testing

WARNING: This page is about a different car, the 2008 GMC Sierra, 2008 GMC Cab & Chassis Sierra, 2008 Chevrolet Silverado, and 2008 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
  1. Test the thermostat for correct operation. Refer to Thermostat Diagnosis .
  2. Test the engine cooling system for overheating. Refer to Engine Overheating .
  3. Inspect the water pump and coolant flow for correct operation. Refer to Water Pump Replacement (LU3)  or Water Pump Replacement (LY6, L76 and L92)  or Water Pump Replacement (LH6, LY2, LY5, and LMG)  or Water Pump Replacement (LMM) .
  4. 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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