The Evaporator sensor located on heater unit detects the core temperature. It is a negative type thermistor whose resistance is inversely proportional to temperature. Evaporator sensor transforms measured temperature into voltage value and delivers it to A/C ECU. when core temperature is blow threshold value, A/C ECU interrupts compressor relay power, in order to prevent evaporator freezing by excessive cooling.
DTC B1242 sets if Evaporator sensor signal is at or over 4.9V for 0.3 seconds.
Item
Detecting Condition
Possible Cause
DTC Strategy
Voltage check
Open in signal circuit
Short to battery in signal circuit
Faulty Evaporator sensor
Faulty Air conditioner control Unit
Enable Conditions
Ignition ON
Threshold value
Evaporator sensor signal is at or over 4.9V for 0.3 seconds
Fail safe
Control with the value of -2?(28.4?)
? Resistance value of incar temp sensor as a function of temperature.
Temperature(?/?)
Resistance(?)
-25/14
43.3
20/68
12.1
0/32
27.6
30/86
8.3
10/50
18
40/104
5.8