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 |
•
Coolant Temperature not reaching warm state | 1. Poor Connector Connection 2. Defected Cooling System 3. Open or Short in ECT Sensor Signal Circuit 4. Defected ECT Sensor |
Enable Conditions |
•
Percentage of fuel cut off phase lower than 20%
•
Percentage of low load phase(Mass air flow less than 5.5 g/sec.(20kg/h) lower than 50%
•
Percentage of high vehicle speed phase (Vehicle speed lower than 87 mph/140 km/h) lower than 90%
•
No high engine speed(higher than 4800 RPM) with vehicle stopped
•
36℉(20℃) decrease on IAT compared to IAT at start
•
Battery voltage higher than 11V and lower than 16V
•
ECT at engine start higher than 14℉(-10℃) and lower than 130.64℉(54.8℃)
•
IAT at engine start higher than 14℉(-10℃)
•
Ambient air temperature model higher than 14℉(-10℃)
•
No relevant DTC present | |
Threshold Value |
•
Measured ECT lower than 165.2℉(74℃) when ECT model is higher than 185℉(85℃) | |
Diagnostic Time |
•
10 to 30 Min. depending on ECT at start and driving pattern | |
Mil On Condition |
•
2 Drive Cycles |
