906K, 906M, 907K, 907M, 908K and 908M Compact Wheel Loaders Electrohydraulic System Electrical Power Supply - Test Caterpillar


Electrical Power Supply - Test
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1.1. Machine ECM
2.1. Diagnostic Trouble Code Procedure

Machine ECM

The following is a list of Diagnostic Trouble Codes (DTCs) that are associated with the system voltage of the machine.

Table 1
Machine ECM (MID 71) 
DTC  Code Description  System Response 
168-3  Electrical System Voltage: Voltage above normal  Electronic components may fail due to high voltage. 
168-4  Electrical System Voltage: Voltage below normal  Various devices in the cab, such as the display, joystick or keypad may power off during operation. The ECM may power off and bring the machine to a sudden stop. 

Possible causes for an FMI 3 diagnostic code are:

  • The sensor supply or the ground circuit in the machine harness is open.

  • The signal circuit in the machine harness is shorted to another circuit.

  • The signal circuit in the machine harness is open or the sensor is disconnected.

  • The sensor has failed.

  • The ECM has failed. An ECM failure is unlikely.

Possible causes for an FMI 4 diagnostic code are:

  • The signal circuit in the machine harness is shorted to ground.

  • The sensor has failed.

  • The ECM has failed. An ECM failure is unlikely.


Illustration 1g03464337
Schematic of the Electrical Power Supply

Note: The diagram above is a simplified schematic of the Machine ECM and the Electrical Power Supply connections. The schematic is electrically correct. However, not all of the possible harness connectors are shown. Refer to the latest revision of Electrical Schematic, UENR5407 for prefixes: L66, L77, L88, or Electrical Schematic, UENR5408 for prefixes: Z66, Z77, Z88, or Electrical Schematic, UENR5409 for prefixes: H66, H77, H88.

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.

Table 2
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 3. 
Begin Process For FMI 3 Troubleshooting HERE 
2. Check The System Voltage At The ECM

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

B. At the harness connector for the ECM, insert multimeter probe between power supply and supply return circuit wires

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

D. Measure the voltage. 

The voltage measurement is in the range of 9.0 VDC to 16.0 VDC. 
OK - The voltage measurement of the ECM power supply is in the range of 9.0 VDC to 16.0 VDC. The system voltage is correct.

Proceed to Test Step 5.

NOT OK - The voltage measurement of the ECM power supply is greater than 16.0 VDC.

Repair: The operation of the engine alternator is not correct. Refer to Service Manual, SENR4130 for brushless alternators for further testing and repair procedures for the alternator or change the engine alternator.

Proceed to Test Step 5. 
Begin Process For FMI 4 Troubleshooting HERE 
3. Check The System Voltage At The ECM

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

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

C. DO NOT DISCONNECT the machine harness from the ECM.

D. At the machine harness for the ECM, insert a multimeter probe into the back of connector. Measure the voltage between positive battery and negative battery. 

The voltage measurement is in the range of 9.0 VDC to 16.0 VDC. 
OK - The voltage measurement of the ECM power supply is in the range of 9.0 VDC to 16.0 VDC. The system voltage is correct.

Proceed to Test Step 4.

NOT OK - The voltage measurement of the ECM power supply is lower than 9.0 VDC.

Proceed to Test Step 5. 
4. Check For A Short

A. Disconnect the machine harness J1 and J2 connector from the ECM.

B. At the machine harness connector, measure the resistance from battery positive contacts to all other J1 and J2 contacts. 

The resistance measurement should be greater than 5000 ohms for each measurement. 
OK - The resistance measurement is greater than 5000 ohms for each measurement.

Proceed to Test Step 5.

NOT OK - The resistance measurement is not greater than 5000 ohms for one or more measurements.

Repair: Repair or replace the machine harness.

Proceed to Test Step 5. 
5. Check If The Diagnostic Code Remains

A. Inspect the contacts of the harness connectors and clean the contacts.

B. Reconnect all harness connectors.

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

D. Operate the machine.

E. Check if diagnostic code is active. 

Diagnostic code is no longer present. 
OK - The diagnostic code is no longer active.

Repair: The initial diagnostic code could have been caused by a poor electrical connection or a short at one of the harness connectors. Resume normal machine operation.

STOP

NOT OK - The diagnostic code is active.

Repair: A failure of the Machine ECM is unlikely. If the cause of the diagnostic code is not found, the ECM may have failed. Prior to replacing an ECM, always contact the Technical Communicator for your dealership for possible consultation with AVSpare. This consultation may effect repair time. If the ECM requires replacement, see the Troubleshooting, "ECM - Replace" section of this manual for additional information.

STOP 

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