This subject is associated with the power connection between the alternator and battery to power the control modules. The primary diagnostic code associated with this title is DTC168, however this title may not be exclusive to DTC168.
| Transmission ECM (MID 81) | ||
|---|---|---|
| DTC | Code Description | System Response |
| 168-3 | Electrical System Voltage: Voltage Above Normal | Activates when the system voltage is above 32.0 VDC. |
| 168-4 | Electrical System Voltage: Voltage Below Normal | Activates when the system voltage is below 18.0 VDC. |
Possible causes for an FMI 3 diagnostic code are:
- The output of the alternator is above normal.
- The signal circuit in the machine harness is shorted to another circuit.
- An external battery source is connected to the electrical circuit.
- The Transmission ECM has failed or the operating software is not the latest version. A failure of the ECM is unlikely.
Possible causes for an FMI 4 diagnostic code are:
- The output of the alternator is below normal.
- The Transmission ECM fuse is open.
- An open circuit or poor connections in the system voltage supply circuit.
- The Transmission ECM has failed or the operating software is not the latest version. A failure of the ECM is unlikely.
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| Illustration 1 | g03651739 |
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Schematic for the Power Supply for the Transmission ECM | |
Note: The diagram above is a simplified schematic of the System Voltage connections. The schematic is electrically correct. However, not all of the possible harness connectors are shown. Refer to: Electrical Schematic, UENR4996, "844K Wheel Dozer (T4F) Electrical System Schematic". Electrical Schematic, UENR1697, "844K Wheel Dozer (LRC) Electrical System Schematic"
This subject is associated with the power connection between the alternator and battery to power the control modules. The primary diagnostic code associated with this title is DTC168, however this title may not be exclusive to DTC 168.
| Implement ECM (MID 82) | ||
|---|---|---|
| DTC | Code Description | System Response |
| 168-3 | Electrical System Voltage: Voltage Above Normal | Activates when the system voltage is above 32.0 VDC. |
| 168-4 | Electrical System Voltage: Voltage Below Normal | Activates when the system voltage is below 18.0 VDC. When system voltage is too low, the ECM will put the hydraulics in shutdown mode. |
Possible causes for an FMI 3 diagnostic code are:
- The output of the alternator is above normal.
- The signal circuit in the machine harness is shorted to another circuit.
- An external battery source is connected to the electrical circuit.
- The Implement ECM has failed or the operating software is not the latest version. A failure of the ECM is unlikely.
Possible causes for an FMI 4 diagnostic code are:
- The output of the alternator is below normal.
- The Implement ECM fuse is open.
- An open circuit or poor connections in the system voltage supply circuit.
- The Implement ECM has failed or the operating software is not the latest version. A failure of the ECM is unlikely.
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| Illustration 2 | g03651740 |
|
Schematic for the Power Supply for the Implement ECM | |
Note: The diagram above is a simplified schematic of the System Voltage connections. The schematic is electrically correct. However, not all of the possible harness connectors are shown. Refer to: Electrical Schematic, UENR4996, "844K Wheel Dozer (T4F) Electrical System Schematic". Electrical Schematic, UENR1697, "844K Wheel Dozer (LRC) Electrical System 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. Check the wiring for pinch points or abrasions. Look for and repair areas that indicate wires are exposed. If a problem with a connection is found, correct the problem and verify that this diagnostic code is active before performing a troubleshooting procedure.
| Troubleshooting Test Steps | Values | Results |
|---|---|---|
| 1. Identify Active FMI Code Associated With The System Voltage Circuit | Code present. |
FMI 3 diagnostic code, proceed to Test Step 2. FMI 4 diagnostic code, proceed to Test Step 4. |
| Begin Process For FMI 3 Troubleshooting HERE | ||
| 2. Check The Battery Voltage A. Start the engine. B. Clear the diagnostic code using the Information Display or Cat ET. C. Operate the machine. D. Review the diagnostic code list for DTC 168-3. |
DTC 168-3 is no longer active. |
OK - The diagnostic code is no longer active. Repair: Return machine to service and monitor for future recurrence of DTC 168-3. STOP NOT OK - DTC 168-3 is active. The charging system is delivering excessive voltage. Repair: The charging system is charging at an excessive voltage. Check the charging system components. See Special Instruction, SEHS0354, "Charging System Troubleshooting". Proceed to Test Step 3, if the check of the system is unsuccessful. STOP |
| 3. Check For A Short Circuit A. Turn the key start switch and disconnect switch to the OFF position. B. Disconnect the harness from the alternator and the ECM. C. Measure the resistance between the alternator "R" terminal and all the harness contacts used for the charging system. |
All resistance readings are greater than 5K Ω. |
OK - The resistance readings are all greater than 5K Ω. The ECM may have failed. Proceed to Test Step 6. NOT OK - One or more of the resistance measurements are less than 5 Ω. The harness contains a shorted connection. Repair: |
| Begin Process For FMI 4 Troubleshooting HERE | ||
| 4. Check The Battery Voltage A. Start the machine and run at high idle for several minutes. B. Measure the battery voltage at the battery posts. |
Battery voltage is greater than 18 VDC. |
OK - Battery voltage is greater than 18 VDC. Battery voltage is correct. Proceed to Test Step 5. NOT OK - Battery voltage is less than 18 VDC Repair: The charging system is not operating correctly. Check the charging system. See Special Instruction, SEHS0354, "Charging System Troubleshooting". STOP |
| 5. Check The Battery Voltage A. The engine must still be running at high idle. B. With the machine harness remaining connected, prepare to make a voltage measurement at the J1 connector at the ECM with a multimeter probe. C. At the machine harness for the ECM, insert the probe into the back of the J1 connector. Measure the voltage (VDC) between a pair of the negative and positive unswitched battery locations. Identify the unswitched battery locations from the schematic above. |
Voltage is greater than 18 VDC. |
OK - Voltage is greater than 18 VDC. Battery voltage is correct. Proceed to Test Step 6. NOT OK - Voltage is less than 18 VDC. Repair: The machine harness is not correct. Repair the machine harness or replace the machine harness. STOP |
| 6. Check If The Diagnostic Code Is Still Active A. Inspect the harness connectors. Clean the contacts of the harness connectors and check the wires for damage to the insulation that is caused by excessive heat, corrosion, or chafing. B. Perform a C. Reconnect all harness connectors in order to make sure that the connectors are fully seated. Also, make sure that the clips for each connector are fastened. D. Turn the disconnect switch and the key start switch to the ON position. E. Operate the machine. F. Determine if the diagnostic code is active. |
The diagnostic code is not active. |
OK - The diagnostic code is not active. The initial diagnostic code was probably caused by a poor electrical connection. The problem does not exist at this time. Resume normal machine operation. STOP NOT OK - The diagnostic code is active. The problem has not been corrected. Repair: Exit this procedure and perform the diagnostic code procedure again. If the problem persists, the ECM may have failed. Prior to replacing to the ECM, contact the local dealership for possible consultation with Caterpillar. This consultation may greatly reduce repair time. See Troubleshooting, "ECM - Replace". STOP |