P0128

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

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

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 Result (Mode 06 Data):

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

Step 1 - 2:

Step 3:

INSPECTION PROCEDURE

HINT: Read freeze frame data using the hand-held tester or the OBD II scan tool. Freeze frame data records the engine conditions when a 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.