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Home >> Cadillac >> 2009 >> DTS 4.6 9 >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System & Fuel System - 4.6L - DTC P0016 To DTC P0336 >> DTC P0128 >> Circuit/System Verification
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Circuit/System Verification

  1. Turn OFF the ignition.
  2. Inspect the cooling system surge tank for the proper engine coolant level. Refer to Cooling System Leak Testing and Cooling System Draining and Filling (Vac-N-Fill) or Cooling System Draining and Filling (Static Fill) .
  3. If the ignition has been OFF for 8 hours or more, the ECT and the IAT should be within 15°C (27°F) of each other and also the ambient temperature. Turn ON the ignition, with the engine OFF, and use a scan tool to observe the IAT and the ECT sensor parameters.
  4. Use the scan tool to verify the proper operation of the engine cooling system fans.
  5. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.
    6. IMPORTANT: A critical analysis of the operation of the thermostat is necessary to properly diagnose this DTC.
  6. Verify the proper heat range, and the operation of the thermostat. Refer to Thermostat Diagnosis .
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