Perkins NJ Series Troubleshooting Manual page 182

182
Troubleshooting Section
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 circuit. The connections
for the unswitched +battery may be routed through a
dedicated protection device (circuit breaker).
Some applications may be equipped with an
engine protection shutdown system or an idle timer
shutdown system that interrupts electrical power
to the keyswitch. 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. These devices may
also shut down the engine.
Usually, battery power to the diagnostic connector
is available and the battery power to the data link
connector is independent of the keyswitch. Therefore,
you will be able to power up the Perkins Electronic
Service Tool (EST), but you may not be able to
communicate 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 Perkins
EST if the keyswitch is in the OFF position. This is
normal.
For intermittent faults such as intermittent shutdowns
that could be caused by the application wiring,
temporarily bypassing the application wiring may be
an effective means of determining the root cause. If
the symptoms disappear with the bypass wiring, the
application wiring is the cause of the fault. A means
of bypassing the application wiring is explained in
this test procedure. This is especially important for
applications that do not provide dedicated circuits
for the unswitched battery and the connections for
the keyswitch.
SENR9982-01