KEY 5T6255 - Caterpillar

Table 1
Diagnostic Trouble Codes for the Electrical Power Supply Circuit
J1939 Code Code Description Notes
168-3 Battery Potential / Power Input 1 : Voltage Above Normal This code indicates that the battery circuit to the ECM has excessive voltage while the engine is running.
The ECM detects the following conditions:
The battery voltage is high for at least 5 seconds.
The keyswitch is in the ON position.
The engine is not cranking.
The warning lamp will come on.
168-4 Battery Potential / Power Input 1 : Voltage Below Normal This code indicates that the battery circuit for the ECM has low voltage while the engine is running.
The ECM detects the following conditions:
The battery voltage is low for at least 5 seconds.
The keyswitch is in the ON position.
The engine is not cranking.
The ECM will normally log the diagnostic code. If battery voltage disappears without returning, the ECM will not log this diagnostic code and the engine will shut down.
The engine may experience changes in the engine rpm, and intermittent engine shutdowns or complete engine shutdowns while the conditions that cause this diagnostic code are present. Battery+ voltage is supplied through P1: 1, 3, and 5. The battery- is supplied through P1: 2, 4, and 6. The ECM receives the keyswitch signal at P1:54 when the keyswitch is in the ON position or in the START position. When the ECM detects battery voltage at this input, the ECM will activate the main relay. When battery voltage is removed from this input, after a short time (up to 60 seconds) the ECM will deactivate the main relay.The cause of an intermittent power supply to the ECM can occur on either the positive side or on the negative side of the battery supply circuit.Usually, battery power to the diagnostic connector is available and the battery power to the data link connector is independent of the keyswitch. Therefore, although the electronic service tool can be powered up, there may be no communication with the engine ECM. The engine ECM requires the keyswitch to be in the ON position in order to maintain communications. The ECM may power down a short time after connecting the electronic service tool if the keyswitch is in the OFF position.
Illustration 1 g03722958
Schematic diagram for the electrical power supply circuit
Not all connectors are shown. Refer to the Electrical Schematic for the application.
Illustration 2 g03722982
View of the pin locations on the P1 connector for the electrical power supply circuit
(1) Battery+
(2) Battery ground
(3) Battery+
(4) Battery ground
(5) Battery+
(6) Battery ground
(8) Start Signal
(28) ECM main relay
(54) Ignition key switch
Table 2
Troubleshooting Test Steps Values Results
1. Inspect Electrical Connectors and Wiring
A. Check the fuses.
B. Thoroughly inspect the battery connections and the connections to the relays. Refer to Troubleshooting, "Electrical Connector - Inspect" for details.
C. Perform a 30 N (6.7 lb) pull test on each of the wires in the ECM connector that are associated with electrical power supply circuit.
D. Check the harness for abrasion and for pinch points from the battery to the ECM.
Damaged wire or connector
Result: A damaged wire or damaged connector was found.