Troubleshooting

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

HINT: This is the purpose of detecting the "thermostat" malfunction.

CIRCUIT DESCRIPTION

DTC Detection Condition:

If the engine coolant temperature (ECT) does not reach 75 °C (167 °F) despite sufficient warm-up time has elapsed.

MONITOR DESCRIPTION

Monitor Strategy:

Typical Enabling Conditions:

Typical Malfunction Thresholds:

Component Operating Range:

Monitor Results (Mode 06 Data):

The ECM estimates the engine coolant temperature (ECT) based on engine starting temperature, engine loads and engine speed. The ECM then compares the estimated ECT with the actual ECT. When the estimated ECT reaches 75 °C (167 °F), the ECM check the actual ECT. If the actual ECT is less than 75 °C (167 °F), the ECM will interpret this as a fault in thermostat or the engine cooling system and set a DTC.

Step 1 - 2:

INSPECTION PROCEDURE

HINT: Read freeze frame data using the hand-held tester or the OBD II scan tool. Freeze frame data records the engine condition when malfunction is detected. When troubleshooting, freeze frame data can help determine if the vehicle was running or stopped, if the engine was warmed up or not, if the air-fuel ratio was lean or rich, and other data from the time the malfunction occurred.