BOSS 3591387 - Caterpillar

Illustration 1 g00352013
(2) Automatic temperature control switch (4) Temperature selection switch (increase) (5) Temperature selection switch (decrease)Press the temperature selection switch (increase) (4), the temperature selection switch (decrease) (5) and the "AUT" switch (2) simultaneously. This will start the diagnostic mode. Display the parameter value that corresponds to the questionable sensor.
Check the sensor reading.
If the sensor reading is correct, the sensor is good.
If the sensor reading is incorrect, go to step 2.
Check the resistance of the sensor. Compare the resistance value to the values on table 1.
If the sensor is not good, replace the sensor.
If the sensor is good, go to step 3.
Table 1
Resistance of Temperature Sensor    
Temperature    Resistance of Coolant Sensor and Sensor in the Cab    Resistance of Sensor for Ambient Air Temperature    
0°C (32°F)     32.6 KOhms     13 -19 KOhms    
10°C (50°F)     19.9 KOhms     7.9 - 11.7 KOhms    
20°C (68°F)     12.5 KOhms     4.8 - 5 KOhms    
25°C (77°F)     10 KOhms     4 KOhms    
30°C (86°F)     8 KOhms     3.1 - 3.3 KOhms    
40°C (104°F)     5.3 KOhms     2.1 - 2.3 KOhms    
Check the wiring harness for high resistance between the sensor and the control module.
If the resistance is greater than 10 ohms, repair the harness or replace the harness.
If the resistance is less than 10 ohms, go to step 4.
Reconnect the sensor and reconnect the control module. Check the readings.
If sensor readings are not correct, replace the control module.
Checking the sensors is completed when the measurements from the sensors are correct.Note: Check the resistance value of the evaporator sensor by placing the sensor in a tub of ice water. The resistance value is 66 K 660 ohms at 0°C (32°F).