P0128

DTC P0128 Thermostat Malfunction

DESCRIPTION

DTC Detection Condition:

HINT:
This DTC relates to the thermostat.
This DTC is set when the Engine Coolant Temperature (ECT) does not reach 75 degrees C (167 degrees F) despite sufficient engine warm-up time.

MONITOR DESCRIPTION

Monitor Strategy:

Typical Enabling Conditions:

Typical Malfunction Thresholds:

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

MONITOR RESULT

Refer to detailed information. Mode 6 Data

Step 1:

Step 1(Continued)-3:

INSPECTION PROCEDURE

HINT: Read freeze frame data using the intelligent tester. Freeze frame data records the engine conditions when malfunctions are 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.