GUIDE AS 6T9564 - Caterpillar

Illustration 1 g01994554
Schematic of the ambient air temperature sensor
Sales models 854K/992K
This diagnostic code is recorded when the ECM reads the sensor signal and the voltage is too low. The possible causes of this failure are listed below:
The sensor has failed.
The signal circuit is shorted to ground.
The ECM has failed.System Response:The failure causes the ambient air temperature to always indicate the maximum temperature or this failure causes the ambient air temperature to intermittently indicate the maximum temperature. Test Step 1. CHECK THE SENSOR.
Turn the disconnect switch and the key start switch to the ON position.
Disconnect the machine harness from the sensor. Expected Result:The diagnostic code changes from CID 0171 FMI 04 to CID 0171 FMI 03. Results:
OK - The diagnostic code changes from "CID 0171 FMI 04" to "CID 0171 FMI 03". Repair: The failure is no longer present. The sensor has failed. perform the Testing and Adjusting, "Pulse Width Modulated (PWM) Sensor-Test" procedure prior to replacing the sensor. STOP
NOT OK - The diagnostic code "CID 0171 FMI 04" is still active. Proceed to test step 2.Test Step 2. CHECK THE HARNESS.
The sensor remains disconnected from the machine harness.
Turn the key start switch and the disconnect switch to the OFF position.
At the harness connector for the sensor, measure the resistance between the signal contact C (wire C453-YL(Yellow)) and frame ground. Expected Result:The resistance is greater than 5000 ohms. STOP. Results:
OK - The resistance is greater than 5000 ohms. The harness circuit resistance is correct. Repair: The ECM has failed. It is unlikely that the ECM has failed. Exit this procedure and perform this procedure again. If the fault is not found, replace the ECM. See Testing and Adjustment, "Module - Replace". STOP
NOT OK - The resistance is less than 5000 ohms. The machine harness has failed. Repair: There is a short between frame ground and the signal circuit in the machine harness. Repair the machine harness or replace the machine harness. STOP