621K OEM Wheel Tractor-Scraper Electrical Power Supply - Test Caterpillar


Electrical Power Supply - Test
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1.1. Implement ECM
2.1. Transmission/Chassis ECM
3.1. Seat ECM
4.1. Suspension System ECM
5.1. Troubleshooting Procedure

Implement ECM

The following is a list of codes that are associated with the system voltage circuit of the Implement ECM.

Table 1
Implement ECM (MID 82) 
DTC  Code Description  System Response 
168-2  Electrical System Voltage : Data erratic, intermittent, or incorrect  The diagnostic code is active when the system voltage is outside the 18 VDC to 32 VDC range for more than a few seconds. 
168-3  Electrical System Voltage : Above Normal  The ECM activates this diagnostic code when the system voltage is above 32.0 VDC. 
168-4  Electrical System Voltage : Below Normal  The ECM activates this diagnostic code when the system voltage is below 18.0 VDC. 

Transmission/Chassis ECM

The following is a list of codes that are associated with the system voltage circuit of the Transmission/Chassis ECM.

Table 2
Transmission/Chassis ECM (MID 27) 
DTC  Code Description  System Response 
168-2  Electrical System Voltage : Data erratic, intermittent, or incorrect  The diagnostic code is active when the system voltage is outside the 18 VDC to 32 VDC range for more than a few seconds. 
168-3  Electrical System Voltage : Voltage Above Normal  The ECM activates this diagnostic code when the system voltage is above 32.0 VDC. 
168-4  Electrical System Voltage : Voltage Below Normal  The ECM activates this diagnostic code when the system voltage is below 18.0 VDC. 

Seat ECM

Table 3
Seat ECM (MID 314) 
DTC  Code Description  System Response 
521219-3  Electrical System Voltage : Voltage Above Normal  The ECM activates this diagnostic code when the system voltage is above 32.0 VDC. 

Suspension System ECM

Table 4
Suspension System ECM (MID 315) 
DTC  Code Description  System Response 
521219-3  Electrical System Voltage : Voltage Above Normal  The ECM activates this diagnostic code when the system voltage is above 32.0 VDC. 

Note: Prior to beginning this procedure, inspect the harness connectors that are involved in this circuit. Poor connections may 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.

Possible Causes for an FMI 2 diagnostic code are:

  • A poor circuit connection to the system ground.

  • A poor circuit connection to system voltage.

  • A charging system component has failed.

  • The ECM has failed. A failure of the ECM is unlikely.

Possible Causes for an FMI 3 diagnostic code are:

  • The alternator output is above normal.

  • The ECM has failed. A failure of the ECM is unlikely.

Possible Causes for an FMI 4 diagnostic code are:

  • The alternator output is below normal.

  • The ECM has failed. A failure of the ECM is unlikely.


Illustration 1g03316878
Illustration of electrical power supply power and ground locations for the Transmission/Chassis ECM.


Illustration 2g03347715
Illustration of electrical power supply power and ground locations for the Implement ECM.


Illustration 3g03502425
Schematic of the sensor supply voltage connections for the Seat ECM


Illustration 4g03502427
Schematic of the sensor supply voltage connections for the Cushion Hitch ECM

Note: The diagrams above are a simplified schematics of the System Voltage connections. The schematics is electrically correct. However, not all of the possible harness connectors are shown. Refer to the following list of electrical schematics for your specific machine:

  • Electrical Schematic, UENR2689 for the 621K Wheel Loader.

Troubleshooting Procedure

Note: Poor harness connections are often the cause of a problem in electrical circuits. Before performing any troubleshooting procedure, inspect all of the connectors involved in the circuit. Verify that all of 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".

Table 5
Troubleshooting Test Steps  Values  Results 
1. Identify Active FMI Code Associated With The System Voltage Circuit. 
Code present. 
FMI 2 diagnostic code, proceed to Test Step 2.

FMI 3 diagnostic code, proceed to Test Step 7.

FMI 4 diagnostic code, proceed to Test Step 8. 
Begin Process For FMI 2 Troubleshooting HERE 
2. Check The System Voltage At The ECM.

A. Turn key start switch and disconnect switch OFF.

B. At the machine harness connector J1 for the ECM, insert a 7X-1710 Multimeter Probe along one of the contacts for power. Insert the other probe to contact frame ground. (See the correct illustration above for the specific machine pin out locations.)

C. Turn key start switch and disconnect switch ON.

D. Start the engine and run the engine at half throttle.

E. Measure the voltage from between the power and return wires.

F. Observe the voltage measurement for the multimeter and wiggle the machine harness connectors of the suspected ECM. Gently pull on the wires and move the wires around.

G. Repeat the step above for another combination of the 24 VDC power connections until all power locations have been checked. 

Voltage is between 18 VDC and 32 VDC. 
OK- Each voltage measurement is between 18 VDC and 32 VDC.

Proceed to Test Step 3.

NOT OK- Each voltage measurement is approximately the same, however, the measurements are unstable. The voltage measurements are showing a large amount of variation. The manipulation of the machine harness and connectors does not affect the measurement.

Proceed to Test Step 5.

NOT OK- The measurement from the +battery contact to frame ground is stable. The voltage is in the range of 18 VDC to 32 VDC. However, the measurement between the ECM +battery contact and the ECM battery (-) contact is not stable 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 to the OFF position.

B. Disconnect the machine harness J1 connector from the ECM.

C. At the J1 harness connector for the ECM, measure the resistance between each of the (-) battery contacts and frame ground. The contacts for the (-) battery connections are illustrated in the connection diagram at the beginning of this procedure. 

Each resistance reading is less than 5 ohms. 
OK- Each resistance measurement is less than 5 ohms. The ground circuit is correct. Reconnect the J1 machine harness connector to the ECM before proceeding to the next test step.

Proceed to Test Step 4.

NOT OK- One or more of the resistance measurements is greater than 5 ohms. There is an open circuit or a poor connection in the ground circuit.

Repair- The open or the possible poor connection is in the ground circuit of the ECM in the machine harness. Refer to the complete Electrical System Schematic of the machine. Check the ground connection located on the rear frame . Ensure that the ground connection is clean, that the ground connection is tight and that the ground connection is in good condition. Check all of the connectors and splice points that are in the ground circuit. Ensure that all connections are clean, that all connectors are secure and that all connectors are in good condition. Repair the machine harness or replace the machine harness.

STOP 
4. Check The Supply Circuits.

A. The key start switch and the disconnect switch remain in the OFF position. The machine harness J1 connector remains disconnected from the ECM.

B. At the J1 harness connector for the ECM, use a length of spare wire to measure the resistance between the alternator "B" terminal and each of the +battery contacts that are connected to the J1 harness connector. The contacts for the +battery connections are illustrated in the connection diagram at the beginning of this procedure. 

Each resistance measures less than 5 ohms. 
OK- Each resistance measurement is less than 5 ohms. The supply circuit is correct. Reconnect the J1 machine harness connector to the ECM before proceeding to the next test step.

Proceed to Test Step 5.

NOT OK- One or more of the resistance measurements is greater than 5 ohms. There is an open circuit or a poor connection in the supply circuit.

Repair- The open or the possible poor connection is in the voltage supply circuit of the ECM in the machine harness. Verify that there are no open circuit breakers or fuses in the circuit.

Refer to the complete Electrical System Schematic of the machine. Check all of the connectors and splice points that are in the supply circuit. Ensure that all connections are clean, that all connections are secure and that all connections are in good condition. Repair the machine harness or replace the machine harness.

STOP 
5. Check the Current Output of the Alternator.

A. Before performing this test step, partially discharge the batteries. The discharge can be done by cranking the engine for approximately 30 seconds without starting the engine. The discharge can also be done by turning on the lights for about 10 minutes without running the engine.

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

C. At the alternator, connect multimeter probes between the alternator "B" terminal and the alternator case (frame ground).

D. Connect a clamp on 8T-0900 AC/DC Clamp-on Ammeter or an equivalent ammeter around the output wire for the alternator.

E. Turn the disconnect switch to the ON position.

F. Start the engine.

G. Run the engine at approximately half throttle.

H. Immediately check the output current of the alternator. 

The output current of the alternator at half throttle is approximately 40 amps, half the alternator full current output rating (80 Amps). The current measurement is stable. 
OK- The output current of the alternator at half throttle is approximately 40 amps and is stable.

Proceed to Test Step 6.

NOT OK- The output current of the alternator at half throttle is not stable. The measurement is showing a large variation of current values. The current output of the alternator is not correct.

Repair- Refer to Service Manual, SENR4130 for brushless alternators for further testing and repair procedures for the alternator.

STOP 
6. Check the Alternator Voltage Output.

A. The multimeter and the ammeter are still connected as used in the last test step. The engine is running.

B. Run the engine for approximately 10 minutes at half throttle.

C. Check the voltage at the alternator output terminal ("B").  

The voltage measurement is 28.0 ± 1.0 VDC.  
OK- The voltage measurement is 28.0 ± 1.0 VDC. The voltage is stable. The voltage output of the alternator is correct.

Proceed to Test Step 10.

NOT OK- The voltage is not stable. There is a large variation in the measured voltage. The voltage output is not correct.

Repair- Refer to Service Manual, SENR4130 for brushless alternators for further testing and repair procedures for the alternator.

STOP 
Begin Process For FMI 3 Troubleshooting HERE 
7. Check The System Voltage At The ECM.

A. Turn key start switch and disconnect switch ON.

B. At the machine harness connector J1 for the ECM, insert a 7X-1710 Multimeter Probe along a contact for power. Insert the other probe along a return contact for power.

C. Start the engine and run the engine at high idle.

D. Measure the voltage from between the power and the return pins at the J1 connector of the ECM.

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.

F. Choose another power and ground connection combination and repeat the process above, if applicable. 

Voltage is between 18 VDC and 32 VDC. 
OK- Voltage is between 18 VDC and 32 VDC.

Proceed to Test Step 10.

NOT OK- The voltage measurement is greater than 32 VDC.

Repair- The operation of the alternator is not correct. Refer to Special Instruction, REHS0354, "Charging System Troubleshooting" for more information.

STOP 
Begin Process For FMI 4 Troubleshooting HERE 
8. Check The Battery Voltage.

A. Start the engine 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 9.

NOT OK - Battery voltage is not greater than 18 VDC.

Repair: The charging system is not correct. Check the charging system. See Special Instruction, REHS0354, "Starting and Charging System".

STOP 
9. Check The System Voltage at the ECM.

A. Turn key start switch and disconnect switch ON.

B. Start the engine and run the engine at high idle.

C. At the machine harness connector J1 for the ECM, insert a 7X-1710 Multimeter Probe along the contact for the sensor power (see main schematic for specific machine). Insert the other probe along the return contact of the sensor.

D. Measure the voltage from between sensor power and sensor ground.

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. 

Voltage is between 18 VDC and 32 VDC. 
OK - Voltage is greater than 18 VDC. The battery system voltage is correct.

Proceed to Test Step 10.

NOT OK - The voltage measurement is less than 18 VDC. The operation of the alternator is not correct.

Repair : A charging system component may be faulty. Check the charging system. Refer to Special Instruction, REHS0354, "Starting and Charging System " for more information.

STOP 
10. Check If The Diagnostic Code Remains.

A. Perform a 45 N (10 lb) pull test on each of the wires associated with the power supply circuit.

B. Reconnect all harness connectors. Make sure that the connectors are fully seated. Observe that the clips for each connector are fastened securely.

C. Turn key start switch and disconnect switch ON.

D. Clear all diagnostic codes.

E. Operate the machine in reverse.

F. Stop machine and engage safety lock lever.

G. Check if diagnostic code for the solenoid is active. 

Code for solenoid is NO longer present. 
OK - Diagnostic code does not exist at this time. Initial diagnostic code may have been caused by poor electrical connection or short at one of the harness connections. Resume machine operation.

STOP

NOT OK - Diagnostic trouble code has not been corrected. Recheck the circuit and perform this procedure again. If the diagnostic code has not been corrected after performing the procedure a second time, follow procedure for replacing the ECM.

Prior to replacing the ECM, always contact the Technical Communication at your dealership for possible consultation with AVSpare. This consultation may greatly reduce repair time.

Follow the steps in Testing and Adjusting, "ECM - Replace" if the ECM needs to be replaced.

STOP 

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