ALARM AS-BACKUP 4548482 - Caterpillar

Illustration 1 g01249620
Schematic of the 5 V sensor supply
The 5 V power supply provides power to the oil level sensor for the transmission.The SPN 3509 FMI 3 diagnostic trouble code is recorded when the ECU reads the voltage of the sensor supply circuit as higher than the normal voltage. The following is a list of possible causes for this diagnostic trouble code:
The sensor supply circuit is shorted to the +battery circuit.
The return circuit is open in the machine harness.
A sensor has failed.
The ECU has failed. This is unlikely.Note: The following test procedure may create other diagnostic trouble codes. Ignore these created diagnostic trouble codes and clear these diagnostic trouble codes when the original diagnostic trouble code has been corrected. Ensure that the diagnostic trouble code of SPN 3509 FMI 3 is active before performing this procedure.Note: Use a digital multimeter for the measurements in this procedure.Test Step 1. CHECK THE VOLTAGE AT THE SENSOR
Turn the disconnect switch and the key start switch to the ON position.
Disconnect the machine harness connector from the sensor.
At the machine harness connector for the sensor, measure the voltage from connector contact 1 (wire 709-OR(Orange)) to connector contact 2 (wire 202-BK(Black)). Measure the voltage from connector contact 1 (wire 709-OR(Orange)) to frame ground. Expected Result:Both voltage measurements are 5.0 0.5 DCV.Results:
OK - Both voltage measurements are 5.0 0.5 DCV. The voltage is correct. Proceed to Test Step 3.
NOT OK - The voltage measurement from connector contact 1 (wire 709-OR(Orange)) to the frame ground is 5.0 0.5 DCV. However, the voltage measurement from connector contact 1 to connector contact 2 is not 5.0 0.5 DCV. The return circuit is faulty in the machine harness.Repair: The return circuit is faulty in the machine harness. Refer to the complete Electrical System Schematic for the vehicle that is being serviced. Examine all connection points in the return circuit for the sensor. Ensure that all connections are clean and secure. Make sure that the connections are in good condition. Repair the machine harness or replace the machine harness.STOP
NOT OK - Both of the voltage measurements are greater than 5.0 0.5 DCV. There may be a short in the machine harness. Proceed to Test Step 2.Test Step 2. CHECK THE HARNESS FOR A SHORT TO THE +BATTERYThe machine harness connector remains disconnected from the sensor.
Turn the disconnect switch and the key start switch to the OFF position.
Disconnect the machine harness connectors J1 and J2 from the ECU.
At the harness connector J1, check the resistance from contact J1-11 (wire 709-OR(Orange)) to all of the other +battery contacts that are connected to the ECU. Expected Result:Each resistance measurement is greater than 5000 ohms.Results:
OK - Each resistance measurement is greater than 5000 ohms. The supply circuit is not shorted to a +battery circuit. Proceed to Test Step 3.
NOT OK - One or more of the resistance measurements is less than 5000 ohms. There is a short in the machine harness.Repair: The power supply circuit is shorted to a +battery