P0128

DTC P0128 - COOLANT THERMOSTAT (COOLANT TEMPERATURE BELOW THERMOSTAT REGULATING TEMPERATURE)

OUTLINE OF DIAGNOSIS
Detect the malfunction of thermostat.
Thermostat open fixing may result in overcooling. Therefore, engine coolant temperature becomes low and the control is unable under theoretical air fuel ratio, so the exhaust deteriorate. Furthermore, it is impossible to perform the other diagnosis if the engine coolant temperature does not rise. For these reasons, thermostat open fixing diagnosis should be conducted.
Judge NG when the estimated engine coolant temperature is higher than engine coolant temperature and the difference between them is large. Judge OK when the engine coolant temperature becomes 75 °C (167 °F) before judging NG.




COMPONENT DESCRIPTION




ENABLE CONDITION

GENERAL DRIVING CYCLE
After starting the engine at cool condition, always perform the diagnosis until the engine coolant temperature becomes more than 75 °C (167 °F).

DIAGNOSTIC METHOD
Judge NG when the estimated engine coolant temperature comes to 75 °C (167 °F) before the engine coolant temperature becomes 75 °C (167 °F) and the difference between them becomes more than 30 °C (86 °F). Judge OK when the engine coolant temperature comes to 75 °C (167 °F) before judging NG.




- Abnormality Judgment
Judge NG when the cumulative time becomes more than 30 seconds after completing all the malfunction criteria .




- Normality Judgment
Judge OK and clear the NG when all the malfunction criteria are completed.

DTC CLEAR CONDITION
- When the OK idling cycle is completed 40 times in a row
- When "Clear Memory" was performed

MALFUNCTION INDICATOR LIGHT CLEAR CONDITION
- When the OK driving cycle is completed 3 times in a row
- When "Clear Memory" was performed

FAIL SAFE
None

ECM OPERATION AT DTC SETTING
- Memorize the freeze frame data. (For test mode $02)
- Memorize the diagnostic value and trouble standard value. (For test mode $06)