150 KENR6933
Troubleshooting Section
i02659963
Ignition Keyswitc h Circuit a nd
Battery Supply Circu it - Test
System Operat
ion Description:
This procedure tests that the correct voltage is being
supplied to th
e Electronic Control Module (ECM).
Use this procedure to troubleshoot the system when
one of the foll
owing diagnostic codes is active or
easily repeated:
•
0168-00 Elect
rical System Voltage high
•
0168-01 Electrical System Voltage low
•
0168-02 Electrical System Voltage erratic,
intermittent, or incorrect
•
1834-02 Ignition Keyswitch loss of signal
The ECM recei
ves electrical power (batte ry
voltage) through the wiring that is supplied by the
manufacturer of the application. Unswitched battery
voltage is su
pplied through P1: 7, 8, 15, 16. The
negative battery is supplied through P1: 1, 2, 3, 9, 10.
The ECM receives the input from the keyswitch at
P1:40whent
he keyswitch is in the ON position or in
the START position. When the ECM detects battery
voltage at this input, the ECM will power up. When
battery vol
tage is removed from this input, the ECM
will power down.
The cause o
f 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 uns
witched battery+ may be routed through a
dedicated protection device (circuit breaker).
Some appl
ications may be equipped with an
engine protection shutdown system or an idle timer
shutdown system that interrupts electrical power
to the 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 t
hese systems will not supply power to the
ECM until one of the following conditions is met:
•
The engi
ne is cranked.
•
The engine oil pressure achieves acceptable limits.
•
An override button is pressed.
Keep in m
ind 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 an
d the battery power to the data link
connector is independent of the keyswitch. Therefore,
youwillbeabletopoweruptheelectronicservice
tool, but you m
ay 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
communicati
ons. The ECM may power down a short
time after connecting the electronic service tool 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,
temporaril
y bypassing the application wiring may be
an effective means of determining the root cause. If
the symptoms disappear with the bypass wiring, the
applicatio
n 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
applicati
ons that do not provide dedicated circuits
for the unswitched battery and the connections for
the keyswitch.
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