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288
TM 9-2320-312-24-2
Troubleshooting Section
Some vehicles may be equipped with an engine
protection shutdown system or an idle timer
shutdown system that interrupts electrical power
to the ECM in order to shut down the engine.
Also, some vehicles may be equipped with an
engine protection shutdown system or an idle timer
shutdown system that interrupts electrical power
to the ignition key switch. The engine protection
shutdown system can be an aftermarket device and
the idle timer shutdown system can be external
to the ECM. Some of these systems will not
supply power to the ECM until one of the following
conditions is met:
The engine is cranked.
The engine oil pressure achieves acceptable
limits.
An override button is pressed.
Keep in mind that these devices may be the cause
of intermittent power to the ECM.
Usually, battery power to the cab data link connector
is available and the battery power to the cab data
link connector is independent of the ignition key
switch. Therefore, you will be able to power up ET,
but you may not be able to communicate with the
engine ECM. The engine ECM requires the ignition
key switch to be in the ON position in order to
maintain communications. The ECM may power
down a short time after connecting ET if the ignition
key switch is in the OFF position. This is normal.
Refer to Troubleshooting, "ATA (SAE J1587 / J1708)
Data Link Circuit - Test".
For intermittent problems such as intermittent
shutdowns that could be caused by vehicle wiring,
temporarily bypassing the vehicle wiring may be
an effective means of determining the root cause.
If the symptoms disappear with the bypass wiring,
the vehicle wiring is the cause of the problem. A
means of bypassing vehicle wiring is explained in
this test procedure. This is especially important for
vehicles that do not provide dedicated circuits for
the unswitched battery and the ignition key switch
connections.

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