An Engine Coolant Temperature Sensor (ECTS) monitors the temperature of the coolant. This input is used by the PCM for engine control and as an enabling criteria for related diagnostics. The air flow coming into the engine is accumulated and used to determine if the engine has been driven within conditions that would allow the engine coolant to heat up normally to the thermostat regulating temperature. If the coolant temperature does not reach regulating temperature of the thermostat, diagnostics that use engine coolant temperature as enabling criteria, may not run when expected.
This DTC will set when there has been excessive time to reach a minimum coolant temperature required for closed loop fuel control.
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 too low for Lambda regulation
Faulty cooling system
Faulty ECT sensor
Poor connection or damaged harness
Enable Conditions
Fuel-cut off phase <20%
Low load phase < 50%
Intake air temperature decrease compared to Start Intake air temperature > -20°C(-4?)
-10?(14?) < Coolant temperature at start < 54.4?(130?)
-10?(14?) < Intake air temperature at start
No high engine speed(4800rpm) with vehicle stopped
No relevant failure
Threshold Value
Measured coolant temp. < 74?(165?) When modelled coolant temp. > 85?(185?)
Diagnostic Time
10~30 min. depending on coolant temperature at start and driving pattern
Mil On Condition
2 Driving Cycles
Temp.(?)
Resistance(?)
-20
14.1 ~ 16.8
40
Approx. 1.2
0
Approx. 5.8
60
Approx. 0.6
20
2.3 ~ 2.6
80
Approx. 0.3
THERMOSTAT
Normal Parameter
Valve Opening Temp
80~84?
Valve Closing Temp.
77?
Full Open Lift
Approx. 8mm(95?)