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Home >> Hummer >> 2008 >> H2 4D Utility Pickup >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls And Fuel - 6.2L - DTC P1255 To DTC P2635 >> DTC P1258 >> Circuit/System Testing
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Circuit/System Testing

  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
  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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