It is a negative type thermistor whose resistance is inversely proportional to temperature. Its output is used for sensor fail-safe, temperature regulation door lock, blower motor level control, mix mode control.
DTC B1238 sets if Ambient Temperature sensor signal is at or over 4.9V for 0.3 seconds.
Item
Detecting Condition
Possible Cause
DTC Strategy
Voltage check
Poor Connection in harness
Open in signal circuit
Shrot to battery in signal circuit
Faulty Ambient Temperature sensor
Faulty air condtioner control Module
Faulty Trip Computer
Enable Conditions
Ignition ON
Threshold value
Ambient Temperature sensor signal is at or over 4.9V for 0.3 seconds
Fail safe
Displayed '--' and A/C control Module regards and controls it as 20?(68?)
? Resistance value of incar temp sensor as a function of temperature.
Temperature(?/?)
Resistance(?)
-20/-4
251
50/122
10
0/32
90
80/140
3.5
25/77
29