Troubleshooting

Table 66
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 en-
gine 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 re-
turning, 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 shut-
downs 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.
UENR0612-07 131
Circuit Tests
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