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 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, ECT not reaching warm state | 1. Poor connection 2. Thermostat |
Enable Conditions |
•
Actual ECT(Engine Coolant Temperature) less than 83℃
•
Integrated air mass greater than 1.4kg
•
AAT(Ambient Air Temperature) greater than -10℃ and less than 57℃
•
ECT(Engine Coolant Temperature) at start greater than -8℃and less than 63℃
•
Difference of IAT(Intake Air Temperature) and IAT at Engine Start greater than -10℃
•
Vehicle speed greater than 12 mph over 15sec
•
Engine Speed greater than 1440 rpm over 15sec | |
Threshold Value |
•
Difference of Modeled ECT and Actual ECT greater than 8℃(46.4°F) | |
Diagnosis Time |
•
10~20min depending on driving pattern | |
Mil On Condition |
•
2 driving cycles. |
