Low Oil Pressure Indicator - Jeep KJ 2005 Service Manual

8J - 26 INSTRUMENT CLUSTER
LOW FUEL INDICATOR (Continued)
turn on the low fuel indicator for the following rea-
sons:
• Bulb Test - Each time the ignition switch is
turned to the On position the low fuel indicator is
illuminated for about three seconds as a bulb test.
• Less Than 15 Percent Tank Full Message -
Each time the cluster receives messages from the
PCM indicating that the percent tank full is less
than 15, the low fuel indicator is illuminated. The
indicator remains illuminated until the cluster
receives messages from the PCM indicating that the
percent tank full has increased to greater than 15.
The PCM applies an algorithm to the input from the
fuel tank sending unit to dampen the illumination of
the low fuel indicator against the negative effect that
fuel sloshing within the fuel tank can have on accu-
rate inputs to the PCM.
• Less Than Empty Percent Tank Full Mes-
sage - Each time the cluster receives a message from
the PCM indicating the percent tank full is less than
empty, the low fuel indicator is illuminated immedi-
ately. This message would indicate that the fuel tank
sending unit input to the PCM is a short circuit.
• More Than Full Percent Tank Full Message
- Each time the cluster receives a message from the
PCM indicating the percent tank full is more than
full, the low fuel indicator is illuminated immedi-
ately. This message would indicate that the fuel tank
sending unit input to the PCM is an open circuit.
• Communication Error - If the cluster fails to
receive a percent tank full message for more than
about twelve seconds, the cluster control circuitry
will illuminate the low fuel indicator until a new per-
cent tank full message is received, or until the igni-
tion switch is turned to the Off position, whichever
occurs first.
• Actuator Test - Each time the cluster is put
through the actuator test, the low fuel indicator will
be turned on, then off again during the bulb check
portion of the test to confirm the functionality of the
LED and the cluster control circuitry.
The PCM continually monitors the fuel tank send-
ing unit input to determine the level of fuel in the
fuel tank. The PCM then applies an algorithm to the
input and sends the proper percent tank full mes-
sages to the instrument cluster. For further diagnosis
of the low fuel indicator or the instrument cluster cir-
cuitry that controls the LED, (Refer to 8 - ELECTRI-
CAL/INSTRUMENT CLUSTER - DIAGNOSIS AND
TESTING).
For proper diagnosis of the fuel tank sending unit,
the PCM, the PCI data bus, or the electronic message
inputs to the instrument cluster that control the low
fuel indicator, a diagnostic scan tool is required.
Refer to the appropriate diagnostic information.
LOW OIL PRESSURE
INDICATOR
DESCRIPTION
Fig. 23 Low Oil Pressure Indicator
A low oil pressure indicator is standard equipment
on all instrument clusters (Fig. 23). This indicator is
located near the lower edge of the instrument cluster,
between the tachometer and the speedometer.
The low oil pressure indicator consists of a stencil-
like cutout of the International Control and Display
Symbol icon for "Engine Oil" in the opaque layer of
the instrument cluster overlay. The dark outer layer
of the overlay prevents the indicator from being
clearly visible when it is not illuminated. A red Light
Emitting Diode (LED) behind the cutout in the
opaque layer of the overlay causes the icon to appear
in red through the translucent outer layer of the
overlay when the indicator is illuminated from
behind by the LED, which is soldered onto the
instrument cluster electronic circuit board. The low
oil pressure indicator is serviced as a unit with the
instrument cluster.
OPERATION
The low oil pressure indicator gives an indication
to the vehicle operator when the engine oil pressure
is low. This indicator is controlled by a transistor on
the instrument cluster electronic circuit board based
upon cluster programming and electronic messages
received by the cluster from the Powertrain Control
Module (PCM) over the Programmable Communica-
tions Interface (PCI) data bus.
The low oil pressure indicator Light Emitting
Diode (LED) is completely controlled by the instru-
ment cluster logic circuit, and that logic will only
allow this indicator to operate when the instrument
cluster receives a battery current input on the fused
ignition switch output (run-start) circuit. Therefore,
the LED will always be off when the ignition switch
is in any position except On or Start. The LED only
illuminates when it is provided a path to ground by
the instrument cluster transistor. The instrument
cluster will turn on the low oil pressure indicator for
the following reasons:
• Bulb Test - Each time the ignition switch is
turned to the On position the low oil pressure indica-
tor is illuminated as a bulb test. The indicator will
remain illuminated until the engine is started
(engine speed is greater than 450 rpm), or until the
ignition switch is turned to the Off position, which-
ever occurs first.
KJ