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Home >> Toyota >> 2004 >> Highlander Limited, FWD >> Repair and Diagnosis >> External Pages >> Different variant/trim >> Section 1 (Engine Control System (SFI) - Diagnostics (2AZ-FE)) >> DTC P0128: Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature) >> Inspection Procedure

Inspection Procedure

WARNING: This page is about a different variant/trim than selected.

HINT:

Read freeze frame data using the hand-held tester or the OBD II scan tool. Freeze frame data records the engine conditions when a malfunction is detected. When troubleshooting, freeze frame data can help determine if the vehicle was running or stopped, if the engine was warmed up or not, if the air-fuel ratio was lean or rich, and other data from the time the malfunction occurred.

  1. CHECK COOLING SYSTEM 
    1. Check the cooling system for excessive cooling, such as abnormal radiator fan operation, modified cooling system and other defects.
    1. NG: REPAIR OR REPLACE COOLING SYSTEM 
    2. OK: GO TO NEXT STEP. 
  2. INSPECT THERMOSTAT (See  INSPECTION  ) 
    1. Check the valve opening temperature of the thermostat.

      OK: Valve opening temperature: 80 to 84°C (176 to 183°F) 

    HINT:

    Also check that the valve is completely closed under opening temperature listed.

    1. NG: REPLACE THERMOSTAT (See  REPLACEMENT  ) 
    2. OK: REPLACE ECM (See  REPLACEMENT  )