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Home >> Jeep >> 2023 >> Grand Cherokee Altitude, AWD >> Repair and Diagnosis >> External Pages >> Different variant/trim >> Section 40 (2.0L - DTCS P0088 To P012D) >> DTC Troubleshooting >> P0128 Thermostat Rationality >> Diagnostic Test

Diagnostic Test

WARNING: This page is about a different variant/trim than selected.
  1. CHECK THE ENGINE COOLANT LEVEL AND CONDITION 
    WARNING:

    Never open the cooling system when the engine is hot. The system is under pressure. Failure to follow these instructions can result in personal injury including extreme burns, scalding, or fatal injury. Allow the engine to cool before opening the cooling system.

    1. Check the engine coolant level and condition in accordance with the Service Information.

      Is the coolant level and condition within specifications?

      Yes 

      • Go To  2

      No 

      • Inspect the vehicle for a coolant leak and add the necessary amount of coolant.

        Perform the POWERTRAIN VERIFICATION TEST. Refer to POWERTRAIN VERIFICATION TEST .

  2. CHECK FOR OTHER DTCS 
    1. Make reference to the recorded DTCs.

      Are there any Engine Coolant Temperature (ECT) or Ambient Air Temperature (AAT) DTCs present?

      Yes 

      No 

      • Go To  3
  3. CHECK THE COOLING SYSTEM OPERATION 
    NOTE:

    If engine coolant temperature is above 65°C (149°F), allow the engine to cool until it is below 65°C (149°F).

    1. Start the engine.
    2. Check for proper operation of the cooling system while the engine warms up to normal operating temperature. Check the Radiator Cap, coolant flow through the Radiator and anything that can cause a lack of system pressure or lack of coolant flow in the system.

      Were any issues found with the cooling system?

      Yes 

      • Make the appropriate repair in accordance with the Service Information.
      • Perform the POWERTRAIN VERIFICATION TEST. Refer to POWERTRAIN VERIFICATION TEST .

      No