Troubleshooting

DTC P0128 Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)

CIRCUIT DESCRIPTION

DTC Detecting Condition:

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 OBD II scan tool or hand-held tester. Because freeze frame records the engine conditions when the malfunction is detected. When troubleshooting, it is useful to determine 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.