Troubleshooting

DTC P0128 COOLANT THERMOSTAT (COOLANT TEMPERATURE BELOW THERMOSTAT REGULATING TEMPERATURE)

CIRCUIT DESCRIPTION

DTC Detection 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 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.