D6T XE Electrical & Hydraulic Troubleshooting Caterpillar

The Power Inverter Control ECM monitors the phase current for the six power transistors located inside the Power Inverter. The Power Inverter Control ECM continuously monitors the phase current from each of the power transistors via the Control Harness. If the Power Inverter Control ECM has an electrical fault, the Machine ECM will disable the Power Train.

Illustration 1	g06092581
(J1) J1 Connector (J2) J2 Connector (A) Motor phase cable connectors (B) Generator phase cable connectors

Power Inverter Control ECM

The following is a list of Diagnostic Trouble Codes (DTCs) associated with the current sensors of the Power Inverter that are monitored by the Power Inverter Control ECM.

Table 1

Power Inverter Control ECM
DTC	Code Description	System Response
2792-3	Generator- Phase A Current Sensor: Voltage Above Normal	The Power Train will be disabled.
2792-4	Generator- Phase A Current Sensor: Voltage Below Normal
2792-5	Generator Phase "A" Current Sensor: Current Below Normal
2793-3	Generator Phase B Current Sensor: Voltage Above Normal
2793-4	Generator Phase B Current Sensor: Voltage Below Normal
2793-5	Generator Phase "B" Current Sensor: Current Below Normal
2794-3	Generator Phase C Current Sensor: Voltage Above Normal
2794-4	Generator Phase C Current Sensor: Voltage Below Normal
2794-5	Generator Phase "C" Current Sensor: Current Below Normal
2789-3	Drive Motor- Phase A Current Sensor: Voltage Above Normal	The Power Train will be disabled.
2789-4	Drive Motor- Phase A Current Sensor: Voltage Below Normal
2789-5	Drive Motor Phase "A" Current Sensor: Current Below Normal.
2790-3	Drive Motor Phase B Current Sensor: Voltage Above Normal
2790-4	Drive Motor Phase B Current Sensor: Voltage Below Normal
2790-5	Drive Motor Phase "B" Current Sensor: Current Below Normal.
2791-3	Drive Motor Phase C Current Sensor: Voltage Above Normal
2791-4	Drive Motor Phase C Current Sensor: Voltage Below Normal
2791-5	Drive Motor Phase "C" Current Sensor: Current Below Normal.

Possible causes for an FMI 3 diagnostic code are:

• Poor connections or faulty connections in the Control Harness connectors

• The sensor circuit is shorted to a higher voltage circuit in the Control Harness.

• The current sensor has failed.

• The ECM has failed. ECM failure is unlikely.

Possible causes for an FMI 4 diagnostic code are:

• Poor connections or faulty connections in the Control Harness connectors

• The sensor signal circuit is open in the Control Harness.

• The sensor signal circuit is shorted to either frame ground or to a ground circuit in the Control Harness.

• The current sensor has failed.

• The ECM has failed. ECM failure is unlikely.

Possible causes for an FMI 5 diagnostic code are:

• Poor connections or faulty connections in the Control Harness connectors

• The sensor signal circuit is open in the Control Harness.

• The current sensor has failed.

• The ECM has failed. ECM failure is unlikely.

Illustration 2	g06109089
Power Inverter Control ECM current sensor connections

The diagram above is a simplified schematic of the Power Inverter Control ECM and the current sensor connections. The schematic is electrically correct. However, not all the possible harness connectors are shown. Refer to the latest revision of the Electrical Schematic, UENR7702 for the complete schematic.

DTC Procedure

Note: Prior to beginning this procedure, inspect the harness connectors involved in this circuit. Poor connections may 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 DTC is active before performing a troubleshooting procedure.

1. Identify the active FMI code associated with the components.

2. Determine which code is present and use the list below to determine which procedure to follow.

• FMI 3 DTC, proceed to Table 2.

• FMI 4 or FMI 5 DTC code, proceed to Table 3.

Table 2

FMI 3 Troubleshooting
Troubleshooting Test Steps	Values	Results
1. Safe Shutdown Procedure This procedure must be performed before service is performed in an area that is near Power Train hazardous voltage components and conductors to ensure that the DC power bus voltage has discharged properly. Reference: Refer to the Troubleshooting, "Electrical Maintenance Guidelines" section of this manual. Perform the "Safe Shutdown Procedure for Electric Drive Tractors" before proceeding with this procedure.	The Safe Shutdown Procedure for Electric Drive Tractors has been performed. DC voltage has been discharged to less than 50.0 VDC.	OK: The Safe Shutdown Procedure for Electric Drive Tractors has been performed. The Monitoring System Display and the Hazardous Voltage Present Lamp indicate that DC voltage is less than 50.0 VDC. The Hazardous voltage has been properly discharged. The power train system for the machine can now be serviced. NOT OK: The DC voltage is greater than 50.0 VDC on the Monitoring System Display or Hazardous Voltage Present Indicator. REPAIR: Wait for at least 10 minutes. Repeat the “Safe Shutdown Procedure for Electric Drive Tractors”. If the voltage is greater than 50.0 VDC, voltage is still present in the system. Measure the voltage between ground and the conductors with a multimeter. Verify that there is less than 50.0 VDC present between all exposed bus contacts before any other action is taken. NOTE: Do not make personal contact with the exposed conductors until you have manually measured for voltage between ground and the conductors. Proceed to Test Step 2.
2. Check For Active DTCs A. Check for active DTCs that need to be resolved prior to troubleshooting this DTC.	The following DTCs should not be active: 2778 2779 2934 2935 3275	OK: The following DTCs are not active: , 2778, 2779, 2934, 2935, or 3275 indicating other components that influence this component are functioning properly. Proceed to Test Step 3. NOT OK: There is an active DTC 2778, 2779, 2934, 2935, or 3275. Any of these DTCs may be the original cause of the DTC and must be repaired first. REPAIR: Refer to the Troubleshooting material for the active DTC and repair that first. After correcting that issue, operate the machine to determine if the cause of the DTC is fixed.
3. Check The Sensor Circuits For A Short A. Disconnect the Control Harness connector from the Power Inverter Control ECM. Disconnect the Power Inverter harness connector. B. Inspect and clean all the contacts of the harness connectors. Ensure that the wires and sockets are secured in the connector. Ensure that the contacts are clean, dry and in good condition. C. Examine the pins on the ECM. Examine the pins on the Power Inverter connector. Ensure that the pins are secured in the connector and are clean, dry, and in good condition. Ensure that none of the pins are bent. D. At the Power Inverter connector, measure the resistance between the sensor signal contact and each of the other Power Inverter contacts.	Each of the resistance measurements between the sensor circuit and all the other circuits used in the harness is greater than 5 KΩ.	OK: Each of the resistance measurements is greater than 5 KΩ. The resistance measurements indicate that the current sensor circuit is not shorted to another circuit in the Control Harness. Proceed to Test Step 4. NOT OK: At least one of the resistance measurements is less than 5 KΩ. There is a short in the Control Harness. REPAIR: The short circuit is between the two circuits registering the low-resistance measurement. There is a problem in the Control Harness. Repair or replace the Control Harness, ensure that the problem has been corrected before operating the machine. Proceed to Test Step 4.
4. Check If The Diagnostic Code Remains A. Reconnect all harness connectors. Return machine to normal operating condition. B. Turn the key switch and the disconnect switch ON. C. Clear all DTCs. D. Operate the machine. E. Stop the machine and engage the parking break. F. Check if the DTC is active.	The diagnostic code is no longer present.	OK: The DTC does not exist currently. The initial DTC may have been caused by poor electrical connection or short at one of the harness connections. Resume machine operation. STOP. NOT OK: The DTV has not been corrected. If the DTC has not been corrected after performing the previous steps a second time, the ECM may need to be flashed with the latest software. Proceed to Test Step 5.
5. Flash The Latest Software To The ECM The software program is unlikely causing this problem. However, flash the latest version of ECM software to the ECM to eliminate this condition as a possible cause. A. To flash the latest software to the Power Inverter Control ECM, refer to the Troubleshooting, "ECM Software - Install" procedure in this manual. After flashing the program, return to this procedure and then proceed to the next step. B. After the latest version of ECM software has been flashed to the ECM, turn the key switch to the OFF position. C. Start the engine. Run the engine at low idle. D. Determine if the DTC is active.	The FMI 3 DTC is not active. No new DTCs or EIDs have been activated.	OK: The FMI 3 DTC is not active. No new DTCs or EIDs have been activated. REPAIR: The latest software version that has been flashed to the ECM has corrected the problem. Resume normal machine operation. STOP. NOT OK: The FMI 3 DTC has been activated again by the ECM. The new software program has not corrected the problem. Proceed to Test Step 6.
6. Check The ECM Operation A. Obtain a spare ECM that can be substituted for the Suspected ECM. The part number of the spare ECM must be the same part number as the Suspected ECM. B. To replace the Suspected ECM with another ECM that has the latest ECM software installed, refer to "ECM - Replace" in this manual. After completing the ECM replacement procedure, return to this procedure and proceed to the next step. C. After the spare ECM has been installed in place of the Suspected ECM and the latest version of ECM software has been flashed, turn the key switch to the OFF position. D. Start the engine. Run the engine at low idle. E. Determine if the DTC is active.	The DTC is not active. No new DTCs or EIDs have been activated.	OK: The DTC is no longer active and no new DTCs or EIDs have been activated. REPAIR: The spare ECM that has been installed in place of the original ECM is operating correctly and no new problems have been detected. The ECM that was replaced appears to have been the cause of the problem. Return the ECM to your parts department for return to Caterpillar for evaluation. Resume normal machine operation. STOP. NOT OK: The DTC has been activated by the replacement ECM. The problem has not been corrected. REPAIR: The activation of the original DTC indicates that the original ECM was not causing the problem. Repeat this "CHECK THE ECM OPERATION" test step and install the original ECM back in place of the "spare" ECM that was installed. The inverter has failed. Repair or replace the inverter. STOP.

Table 3

FMI 4 or FMI 5 Troubleshooting
Troubleshooting Test Steps	Values	Results
1. Safe Shutdown Procedure This procedure must be performed before service is performed in an area that is near any power train hazardous voltage components or conductors to ensure that the DC bus voltage has discharged properly. Reference: Refer to the "Operation and Maintenance Manual" for your machine , Safe Shutdown Procedure to safely shut down the machine.	The Safe Shutdown Procedure has been performed. DC voltage has been discharged to less than 50 VDC.	OK -The Safe Shutdown Procedure has been performed. The monitoring system display and the hazardous voltage indicator indicate that DC voltage is less than 50 VDC. The hazardous voltage has been discharged. The power train system for the machine can now be serviced. NOT OK: The DC voltage is greater than 50 VDC on The monitoring system display or hazardous voltage indicator is illuminated. REPAIR: Wait for period of at least 10 minutes. Repeat the “Safe Shutdown Procedure”. If the voltage is greater than 50 VDC, voltage is still present in the system. Measure the voltage between ground and the conductors with a multi-meter. Verify that there is less than 50 VDC present between all exposed bus contacts before any other action is taken. Proceed to the next test step. NOTE: Do not make personal contact with the exposed conductors until you have manually measured for voltage between ground and the conductors.
2. Check For Active DTCs A. Check for active DTCs that need to be resolved prior to troubleshooting this DTC.	The following DTC should not be active: 3275	OK: The following DTC is not active: 3275 indicating other components that influence this component are functioning properly. Proceed to Test Step 3. NOT OK: There is an active DTC 3275. This DTC may be the original cause of the DTC and must be repaired first. REPAIR: Refer to the Troubleshooting material for the active DTC and repair that first. After correcting that issue, operate the machine to determine if the cause of the DTC is fixed.
3. Check The Sensor Circuit For An Open A. Disconnect the Control Harness from the Power Inverter. B. Disconnect the Control Harness connector J2 from the ECM. C. Inspect and clean all the contacts of the harness connectors. Ensure that the wires and sockets are secured in the connector and the contacts are clean and in good condition. D. At the connector for the Power Inverter, connect a jumper wire between the phase current contact and the ECM ground contact. E. Measure the resistance between the ECM connector and Power Inverter connector for the current phase that logged the DTC. Verify that the jumper wire is making good contact at both of the connection points. F. Observing the multimeter resistance measurement, wiggle the harness connector for the ECM and the harness connector for the Power Inverter. Gently pull and move the wires. Do not disconnect the jumper wire.	Resistance is less than 5.0 Ω	OK: The resistance is less than 5.0 Ω. Proceed to Test Step 4. NOT OK: The resistance measurement is greater than 5.0 Ω always or the resistance measurement is greater than 5.0 Ω some of the time during the manipulation of the harness. REPAIR: The open circuit or the poor connection is in one of the sensor circuits connected by the jumper wire. Repair or replace the Control Harness. STOP.
4. Check The Sensor Circuit For A Short A. The key switch and the disconnect switch remain in the OFF position. B At the Control Harness connector for the ECM, attach one lead to the phase current contact that logged the DTC. Attach the other lead to the Power Inverter connector and the connector for ECM J2. C. Inspect the harness for any areas where the insulation is worn. Inspect the harness for pinch points that may cause a short circuit. D. At the Control Harness connector for the ECM, attach one lead to the phase current contact that logged the DTC. Using the other lead at the connector for the Power Inverter, measure the resistance to all the contacts on that connector. Leave the lead at the ECM connector on the Control Harness and measure the resistance from the Control Harness to the support bracket.	Each of the resistance measurements is greater than 5 KΩ, except the mating contact to the contact being tested, which should be less than 5 KΩ.	OK:Each of the resistance measurements is greater than 5 KΩ, except the mating contact to the contact being tested, which should be less than 5 KΩ. The resistance measurements indicate that the current sensor circuits are not shorted to another circuit or to the Control Harness support bracket in the Control Harness. Proceed to Test Step 5. NOT OK: At least one of the resistance measurements is less than 5 KΩ. There is a short in the Control Harness. REPAIR:The short circuit is between the current sensor signal circuit and the circuit that registered the low-resistance measurement or the short circuit is between the current sensor signal circuit and frame ground. There is a problem in the Control Harness. Repair or replace the Control Harness. After the new Control Harness has been installed, Verify the DTC no longer activates. Proceed to Test Step 6.
5. Check If The DTC Remains A. Reconnect all harness connectors. Return machine to normal operating condition. B. Turn the key switch and the disconnect switch ON. C. Clear all DTCs. D. Operate the machine. E. Stop the machine and engage the parking brake. F. Check if the DTC is active.	The DTC is no longer present.	OK: The DTC does not exist currently. The initial DTC may have been caused by a poor electrical connection or short at one of the harness connections. Resume machine operation. NOT OK: The DTV has not been corrected. If the DTC has not been corrected after performing the previous steps a second time, the ECM may need to be flashed with the latest software. Proceed to Test Step 6.
6. Flash The Latest Software To The ECM The software program is unlikely causing this problem. However, flash the latest version of ECM software to the ECM to eliminate this condition as a possible cause. A. To flash the latest software, refer to the Troubleshooting, "ECM Software - Install" procedure in this manual. After flashing the program, return to this procedure and then proceed to the next step. B. After the latest version of ECM software has been flashed to the ECM, turn the key switch to the OFF position. C. Start the engine. Run the engine at low idle. D. Determine if the DTC is active.	The FMI 4 diagnostic code is not active. No new DTCs or EIDs have been activated.	OK: The FMI 4 diagnostic code is not active. No new DTCs or EIDs have been activated. REPAIR: The latest software version flashed to the ECM has corrected the problem. Resume normal machine operation. NOT OK: The FMI 4 diagnostic code has been activated again by the ECM. The new software program has not corrected the problem. Proceed to Test Step 7.
7. Check The ECM Operation A. Obtain a spare ECM that can be substituted for the Suspected ECM. The part number of the spare ECM must be the same part number as the Suspected ECM. B. To replace the Suspected ECM with another ECM that has the latest ECM software installed, refer to "ECM - Replace" in this manual. After completing the ECM replacement procedure, return to this procedure and proceed to the next step. C. After the spare ECM has been installed in place of the Suspected ECM and the latest version of ECM software has been flashed, turn the key switch to the OFF position. D. Start the engine. Run the engine at low idle. E. Determine if the DTC is active.	The DTC is not active. No new DTCs or EIDs have been activated.	OK: The DTC is no longer active and no new DTCs or EIDs have been activated. REPAIR: The spare ECM that has been installed in place of the original ECM is operating correctly and no new problems have been detected. The ECM that was replaced appears to have been the cause of the problem. Return the ECM to your parts department for return to Caterpillar for evaluation. Resume normal machine operation. NOT OK: The DTC has been activated by the replacement ECM. The problem has not been corrected. REPAIR: The activation of the original DTC indicates that the original ECM was not causing the problem. Repeat this "CHECK THE ECM OPERATION" test step and install the original ECM back in place of the "spare" ECM that was installed. The inverter has failed. Repair or replace the inverter. STOP.