Inspection Procedure

WARNING: This page is about a different car, the 2007 Toyota Prius. However, it is still accessible from the selected car via links, so may be relevant.

HINT:

If DTCs P0115, P0116, P0117, P0118 and P0125 are output simultaneously, engine coolant temperature sensor circuit may be open or shorted. Perform troubleshooting on DTC P0115, P0117 or P0118 first.
Read freeze frame data using the intelligent tester. The ECM records vehicle and driving condition information as freeze frame data the moment a DTC is stored. When troubleshooting, freeze frame data can be helpful in determining whether the vehicle was running or stopped, whether the engine was warmed up or not, whether the air/fuel ratio was lean or rich, as well as other data recorded at the time of a malfunction.

CHECK OTHER DTC OUTPUT (IN ADDITION TO DTC P0125)

Connect the intelligent tester to the DLC3.
Turn the power switch ON (IG).
Turn the intelligent tester ON.
Enter the following menus: DIAGNOSIS / ENHANCED OBD II / DTC INFO / CURRENT CODES.

Read the DTCs using the intelligent tester.

Result

DTC CHART

Display (DTC output)	Proceed to
P0125	A
P0125 and other DTCs	B

HINT:

If any other codes besides P0125 are output, perform troubleshooting for those DTCs first.

B: GO TO DTC CHART

A: Go to next step

INSPECT THERMOSTAT
1. Check the valve opening temperature of the thermostat.
  OK:
  
  Thermostat valve begins to open at temperature of 80 to 84°C (176 to 183°F)
  
  HINT:
  
  Also check that the valve is completely closed at a temperature lower than specified above.
NG: REPLACE THERMOSTAT

OK: REPLACE ENGINE COOLANT TEMPERATURE SENSOR