Troubleshooting

DTC P0128 Thermostat Malfunction

DTC Detection Condition:

CIRCUIT DESCRIPTION
If the water temperature becomes 75 °C (167 °F) or more, it is abnormal.

If not due to the thermostat malfunction, it is abnormal.

Step 1 - 2:

INSPECTION PROCEDURE

HINT: Read freeze frame data using TOYOTA hand-held tester or OBD II scan tool, as freeze frame data records the engine conditions when a malfunction is detected. When troubleshooting, it is useful for determining whether the vehicle was running or stopped, the engine was warmed up or not, the air-fuel ratio was lean or rich, etc. at the time of the malfunction.