LEVER 2106285 - Caterpillar

The diagnostic code is recorded when the interface module indicates that the voltage of the sensor supply circuit is too high, too low, or erratic.Possible causes of an FMI 03 Diagnostic code are:
The output of the sensor supply has shorted to the + battery circuit.
The ECM has failed. A failure of the ECM is unlikely.Possible causes of an FMI 04 Diagnostic code are:
The output of sensor supply has an open circuit.
A sensor has failed.
The ECM has failed. A failure of the ECM is unlikely.Note: Before performing this procedure, verify that all circuit breakers and all fuses in the charging circuit and the ECM system supply circuit are closed. If a problem with a circuit breaker or a fuse is found, correct the problem, and check for codes before proceeding with the following steps.Note: Poor harness connections are often the cause of a problem in electrical circuits. Before performing this procedure, inspect all the connectors involved in the circuit. Verify that all the connections in the circuit are dry, clean, secure, and in good condition. Each pin and socket in the connectors should mate correctly when the connectors are fastened together. Check for exposed wires at the connectors for nicks or abrasion. If a problem is found with any of the connections: correct the problem and verify that diagnostic code is still active, before performing the following procedures. For more information, refer to Troubleshooting, "Electrical Connector - Inspect".Perform a wiggle test on the sensor circuit of the machine wiring harness, using Cat ET. The wiggle test can be used to detect open or shorted connections in the machine wiring harness. Reconnect all harness connectors. Make sure that the connectors are fully seated. Observe that the clips for each connector are fastened. For more information, refer to Troubleshooting, "Electrical Connector - Inspect".
Illustration 1 g06112609
Machine ECM J1 Sensor Supply connections
Illustration 2 g06112617
Machine ECM J2 Sensor Supply connections
Illustration 3 g06141349
Secondary ECM Sensor Supply connections
Note: The diagrams above are a simplified schematic of the Machine ECM connections. The diagrams are electrically correct. However, not all the possible harness connectors are shown. Refer to the latest revision of the Electrical Schematic for the complete schematic.
Table 2
Troubleshooting Test Steps Values Results
1. Identify The Active FMI Code Associated With The Sensor Supply Circuit Code present FMI 3 diagnostic code, proceed to Test Step 3.
FMI 4 diagnostic code, proceed to Test Step 5.
2. Check The Voltage At The ECM
A. Turn the key start switch and the battery disconnect switch to the OFF position.
B. At the machine harness connector for the ECM, insert a 7X-1710 Multimeter Probe along the contact for the sensor power. Insert another probe along the return contact for the sensor power.
C. Turn the disconnect switch to the ON position.
E. Observe the voltage measurement for the multimeter and wiggle the machine harness connectors of the Machine ECM. Gently pull on the wires and move the wires around.
See the schematic to determine the voltage that is applicable to each circuit. OK - The voltage is appropriate for the