A water temp sensor located at heater unit detects coolant temperature. It contains negative type themistor whoses resistance value is in inverse proportion to temperature. Resistance of watersensor that varies with temperature makes signal voltage of A/C ECU change. In this way A/C ECU detects temperature. Signal of water sensor is used for cold engine lockout control - When the driver operates the heater before the engine is warmed up enough, to prevent driver from unpleasantness of cold air. the heater control unit reduces blower motor speed until coolant temperature reaches the threshold value -
The ECM sets DTC B1203 if there is a short circuit in water temp sensor signal harness or the measured voltage value of the sensor is less than the threshold value(0.1V)
Item | Detecting Condition | Possible Cause |
DTC Strategy | ● Voltage check | ● Short Circuit in signal harness ● Faulty water temp. Sensor ● Faulty A/C Control Unit |
Threshold value | ● <0.1V | |
Detecting time | ● 0.3sec | |
FAIL SAFE | ● Control with the value of -2℃ |
※ Resistance value of water temp sensor as a function of temperature.
Temperature(℃) | Resistance(㏀) | Temperature(℃) | Resistance(㏀) |
-10 | 55.85 | 40 | 5.31 |
0 | 32.91 | 60 | 2.48 |
20 | 12.51 | 80 | 1.25 |
