P0128

DTC P0128 Thermostat Malfunction

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

DESCRIPTION

DTC Detection Condition:

This DTC is output when the Engine Coolant Temperature (ECT) does not reach 75 °C (167 °F) despite sufficient engine warm-up time.

MONITOR DESCRIPTION

Monitor Description:

Monitor Strategy:

Typical Enabling Conditions:

Typical Malfunction Thresholds:

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. 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 engine cooling system or thermostat and set a DTC.

Step 1-3:

Step 3(Continued):

INSPECTION PROCEDURE

HINT: Read freeze frame data using the intelligent tester. The ECM records vehicle and driving condition information as freeze frame data the moment a DTC is stored. When troubleshooting, freeze frame data can be helpful in determining whether the vehicle was running or stopped, whether the engine was warmed up or not, whether the air/fuel ratio was lean or rich, as well as other data recorded at the time of a malfunction.