COUPLING 6Y4771 - Caterpillar

Transmission ECM
The following is a list of codes that are associated with the system voltage circuit of the machine.
Table 1
Transmission ECM (MID 027)
DTC Code Description System Response
168-04 Electrical System Voltage: Voltage Below Normal The ECM activates this diagnostic code when the system voltage is below 18 VDC. Possible Causes for an FMI-04 diagnostic code are:
The alternator output is below normal.
The Transmission ECM has failed (unlikely).
Illustration 1 g03238338Note: 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 the Electrical Schematic, UENR3186.Diagnostic Trouble Code Procedure
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.
Table 2
Troubleshooting Test Steps Values Results
1. Identify Active FMI Code Associated With The System Voltage Circuit
Code present. An FMI-04 diagnostic code is present. Proceed to Test Step 2.
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 J1 harness connector for the Transmission ECM, measure the supply voltage. Insert the positive probe along one of the positive power supply circuit wires at contact J1-31. Insert the negative probe along one of the supply return circuit wires at contact J1-13.
C. Start the engine and run the engine at high idle.
D. Measure the voltage between contact J1-31 and contact J1-13.
Voltage is between 18 VDC and 32 VDC. OK - The voltage measurement of the ECM power supply is in the range of 18 VDC to 32 VDC. The system voltage is correct. There does not appear to be a problem with the alternator or the machine power supply circuits.
Proceed to Test Step 3.
NOT OK -The voltage measurement of the ECM power supply is less than 18 VDC.
Repair : A charging system component may be faulty. Check the charging system. Refer to Special Instruction, REHS0354, "Charging System Troubleshooting" for more information.
STOP
3. Check the status of the diagnostic code
A. Turn the disconnect switch and key start switch to the OFF position.
B. Reconnect any harness connectors that were disconnected and checked.
C. Turn key start switch and disconnect switch ON.
D. Start the engine and run the engine at high idle.
E. Determine if the FMI-04 DTC is active.
The FMI-04 DTC is not active. OK - DTC does not exist at this time. 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 FMI-04 DTC is still active. The DTC has not been corrected.
Repair: If the system voltage is correct and the ECM is still activating this DTC, the ECM could be causing the problem. Ensure that the latest version of software