STRAINER 0812933 - 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 Chassis ECM has failed. The ECM failing 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 Chassis ECM has failed. This situation is unlikely.
Illustration 4 g06042606
Chassis ECM sensor supply circuits
Note: The diagram above is a simplified schematic of the Chassis ECM connections. The schematic is electrically correct. However, not all of the possible harness connectors are shown. Refer to the latest revision of Electrical Schematic, UENR6735 (MH3295) for the complete schematic.Diagnostic Trouble Code Procedure
Note: Prior to beginning this procedure, inspect the harness connectors that are involved in this circuit. Poor connections can often be the cause of a problem in an electrical circuit. Verify that all connections in the circuit are clean, secure, and in good condition. If a problem with a connection is found, correct the problem and verify that the diagnostic code is active before performing a troubleshooting procedure. For sensors powered via the fuse panel, check the condition of the appropriate fuse before beginning the troubleshooting procedure.
Table 5
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 2.
FMI 4 diagnostic code, proceed to Test Step 4.
FMI 6 diagnostic code, proceed to Test Step 5.
Begin Process For FMI 3 Troubleshooting HERE
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 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 circuit as determined by the schematic.
Proceed to Test Step 3.
NOT OK - The voltage measurement is unstable. The voltage measurement is showing a large amount of variation. The manipulation of the machine harness and connectors does not affect the measurement.
Proceed to Test Step 7.
NOT OK - The voltage measurement is stable and within the specified range. However, the measurement between the ECM + battery contact and the ECM (-) battery contacts are not stable or in the correct range at all times.
Proceed to test step 3.
3. Check The Ground Circuits
A. Turn the key start switch and the disconnect switch OFF.
B. Disconnect the machine harness from the ECM.
C. At the ECM harness connector, measure the resistance between each of the return wires and frame ground.
The resistance is less