An open stuck thermostat means an increase of the engine warm up time and can cause emission increase as well. To detect open stuck thermostat, the ECM/PCM checks measured coolant temperature as soon as calculated coolant temperature reaches threshold and sets DTC P0128 when measured coolant temperature is lower than threshold. If same code is set again in the next driving cycle, MIL is illuminated.
Item | Detecting Condition | Possible Cause |
DTC Strategy |
•
Thermostat open stuck monitor | 1. Poor connection 2. Short to ground in signal circuit 3. ECTS |
Enable Conditions |
•
Modeled ECT - Actual ECT > 8 ℃
•
Integrated air mass > 1.4 kg/h
•
-8 ℃ < ECT at start < 57 ℃
•
IAT - IAT at Engine Start > -10 ℃
•
[Vehicle speed > 12 MPH & Engine RPM > 1440 RPM] > 15 sec. | |
Threshold Value |
•
Actual ECT < 75 ℃ | |
Diagnosis Time |
•
- | |
Mil On Condition |
•
2 trips |
