Troubleshooting

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

CIRCUIT DESCRIPTION

DTC Detection Condition:

If the engine coolant temperature does not reach 75°C (167°F) even after warming up, it is abnormal.

HINT: This is the procedure of the "thermostat".

Step 1 - 2:

INSPECTION PROCEDURE

HINT: Read freeze frame data using the hand-held tester or the 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.