CX28 Transmission For Combat and Tactical Vehicles Transmission ; Transfer Case Electronic Control System Caterpillar

Illustration 1	g02305953
Schematic of the 5 V sender supply

The 5 V power supply provides power to the transfer case oil temperature sender. The FMI 4 is recorded when the ECU reads the voltage of the signal wire as being below normal and/or shorted to ground.

The following is a list of possible causes for this diagnostic trouble code:

• The sender supply circuit is shorted to the ground.

• A sender has failed.

• The ECU has failed. The ECU failing 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 441 FMI 4 is active before performing this procedure.

Note: Use a digital multimeter for the measurements in this procedure.

Test Step 1. CHECK THE SENDER

1. Turn the key start switch and the disconnect switch to the ON position.

2. Disconnect the machine harness from the sender. Then, observe the status of the diagnostic trouble code.

Expected Result:

The diagnostic trouble code is not active.

Results:

• OK - The diagnostic trouble code is not active. The harness circuit is correct. The sender that was disconnected has failed.

  Repair: Replace the sender.

  STOP

• NOT OK - The diagnostic trouble code is still active. The machine harness may be shorted to ground. Proceed to Test Step 2.

Test Step 2. CHECK FOR A SHORT TO GROUND

1. Turn the key start switch and the disconnect switch to the OFF position.

2. Disconnect the machine harness from the ECU.

3. At the harness connector for the ECU, measure the resistance between frame ground and contact J2-11 (wire 493-PU) of the sender supply circuit.

Expected Result:

The resistance is greater than 5000 ohms.

Results:

• OK - The resistance is greater than 5000 ohms. The harness circuit resistance is correct. The ECU may have failed.

  Repair: Check the circuit again. If the Caterpillar Electronic Technician (ET) is available, use the Cat ET service tool in order to perform a "Wiggle Test" on the machine wiring harness. The "Wiggle Test" can detect shorts and opens in the machine wiring harness that are momentary or intermittent. It is unlikely that the ECU has failed. Exit this procedure and perform this procedure again. If the cause of the diagnostic trouble code is not found, replace the ECU. Prior to replacing an ECM, always contact your dealership for possible consultation with Caterpillar. This consultation may greatly reduce repair time. See Testing and Adjusting, "Electronic Control Unit - Replace".

  STOP

• NOT OK - The resistance is less than 5000 ohms. The machine harness has failed.

  Repair: The 493-PU wire is shorted to ground in the machine harness. Refer to the complete Electrical System Schematic for your machine. Check all harness connectors that are in the power supply circuit. Ensure that the connectors are clean and secure. Repair the machine harness or replace the machine harness.

  STOP