DTC P0128: Thermostat Malfunction: Procedure

1. Connect the Techstream to the DLC3.
2. Enter the following menus: Powertrain / Engine / Trouble Codes.
3. Read the DTCs.

   Result

   Result	Proceed to
   P0128	A
   P0128 and other DTCs	B

   HINT: 

   If any other codes besides P0128 are output, perform the troubleshooting for those DTCs first.

B → See step   4 

A: Go to next step 

1. Check for defects in the cooling system that might cause the system to be too cold, such as an abnormal radiator fan operation or a modified cooling system.
2. Check the valve opening temperature of the thermostat.

   Standard

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

   HINT: 

   Also check that the valve is completely closed below the opening temperature shown above.

NG → REPAIR OR REPLACE COOLING SYSTEM 

OK: Go to next step 

1. Inspect the thermostat. Refer to INSPECTION .

NG → See step   5 

OK → See step   6