The Engine Coolant Temperature Sensor (ECTS) is located in the engine coolant passage of the cylinder head for detecting the engine coolant temperature. The ECTS uses a thermistor whose resistance changes with the temperature. The electrical resistance of the ECTS decreases as the temperature increases, and increases as the temperature decreases. The reference 5 V in the PCM is supplied to the ECTS via a resistor in the PCM. That is, the resistor in the PCM and the thermistor in the ECTS are connected in series. When the resistance value of the thermistor in the ECTS changes according to the engine coolant temperature, the output voltage also changes. During cold engine operation the PCM increases the fuel injection duration and controls the ignition timing using the information of engine coolant temperature to avoid engine stalling and improve drivability.
Checking output signals from ECTS under detecting condition, if an output signal is intermittently above 4.9V, PCM sets P1115.
Item | Detecting Condition | Possible Cause |
DTC Strategy | ● Monitor the signal of ECTS | ● Poor Connection ● Open or short to battery in signal circuit ● Open in ground circuit ● Faulty ECTS ● Faulty PCM |
Enable Conditions | Case 1 | ● Time after start-up > 120 sec. |
Case 2 | ● Time from IG "OFF" to IG "ON" > 360 min. ● Intake air temperature ≥ -10℃(14℉) ● Engine running state | |
Threshold value | ● Intermittently engine coolant temperature sensor’s voltage > 4.9V | |
Diagnosis Time | ● Continuous | |
MIL On Condition | ● DTC only (NO MIL ON) |
Temp. (°C/°F) | Resistance (kΩ) | Temp. (°C/°F) | Resistance (kΩ) |
-40(-40) | 48.14 | 40(104) | 1.15 |
-20(-4) | 14.13 ~ 16.83 | 60(140) | 0.59 |
0(32) | 5.79 | 80(176) | 0.32 |
20(68) | 2.31 ~ 2.59 |
Fig 1) Temperature : 180℉
The output signals of IATS & ECTS change smoothly without any rapid changes. Those have almost same characteristic signal during the early period after start. It means that the temperatures of intake air and engine coolant are depended on the temperature of atmosphere. Meanwhile, during the warming up, the output signal of ECTS is going up increasingly. but, the output signal of IATS changes a little bit. even it may not change almost. It means that the heat of engine does not affect on the temperature of intake air.
