ule (ECM) over the Controller Area Network (CAN)
data bus. The low oil level 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 detects that the ignition switch is in the On
position. Therefore, the LED will always be off when
the ignition switch is in any position except On. 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 level indi-
cator for the following reasons:
• Bulb Test - Each time the ignition switch is
turned to the On position the low oil level indicator
is illuminated for about two seconds as a bulb test.
• Engine Oil Level Low Message - Once the
engine has been started, each time the cluster
receives a message from the ECM indicating that the
engine oil level is at or near the “Minimum” mark on
the dipstick, the low oil level indicator is illuminated.
The indicator remains illuminated briefly at first, but
will remain illuminated for longer periods as subse-
quent messages indicate that the oil level has
dropped further. Eventually, the indicator will
remain illuminated solid until the engine oil level is
corrected, or until the ignition switch is turned to the
Off position, whichever occurs first.
The instrument cluster also supplements the oil level
indicator by displaying an engine oil icon along with
alpha-numeric messages in the multi-function indicator
Liquid Crystal Display (LCD) advising the vehicle oper-
ator how much oil is required to correct the engine oil
level, and when the “Maximum” engine oil level has
been exceeded. See the owner’s manual in the vehicle
glove box for more information on this feature.
The ECM continually monitors the engine oil level
and temperature sensor to determine the engine oil
level. The ECM then sends the proper engine oil
level messages to the instrument cluster. If the
instrument cluster turns on the indicator after the
bulb test, even after the engine oil level is sufficient,
it may indicate that the engine or the engine oiling
system requires service. For proper diagnosis of the
engine oil level and temperature sensor, the ECM,
the CAN data bus, or the electronic message inputs
to the instrument cluster that control the low oil
level indicator, a DRBIIIt scan tool is required. Refer
to the appropriate diagnostic information.
MAINTENANCE INDICATOR
DESCRIPTION
An Active Service SYSTem (ASSYST) engine oil main-
tenance indicator is optional equipment on all instru-
ment clusters. In vehicles so equipped, a second,
dedicated ASSYST microprocessor is integral to the
cluster electronic circuit board. The ASSYST indications
are displayed and can be toggled with the clock indica-
tion on the right side of the multi-function indicator
Liquid Crystal Display (LCD) located near the lower
edge of the instrument cluster, directly below the speed-
ometer. The ASSYST displays include numeric values
combined with several icons to indicate actual engine oil
level, and reminders in time (days) or distance (miles or
kilometers) until the next required engine oil mainte-
nance is anticipated. ASSYST also provides several
audible indications using the electronic tone generator
on the instrument cluster circuit board to supplement
these visual displays.
The indications of the ASSYST engine oil mainte-
nance indicator are not visible when the LCD is not illu-
minated. When illuminated, the ASSYST indications
appear as dark characters and icons silhouetted against
an amber field. When the exterior lighting is turned Off,
the display is illuminated at maximum brightness.
When the exterior lighting is turned On, the display
illumination level can be adjusted in concert with the
cluster general illumination lighting using the “+” (plus)
and “2” (minus) multi-function indicator push buttons.
The ASSYST engine oil maintenance indicator is ser-
viced as a unit with the instrument cluster.
OPERATION
The ASSYST engine oil maintenance indicator micro-
processor uses numerous criteria besides time and mile-
age to evaluate vehicle maintenance requirements. Time
data is taken from the electronic digital clock integral to
the instrument cluster. Vehicle distance data is obtained
from the Controller Antilock Brake (CAB) over the Con-
troller Area Network (CAN) data bus. Coolant tempera-
ture, engine oil temperature, engine oil level, engine oil
quality, engine speed, and engine load data are obtained
from the Engine Control Module (ECM) over the CAN
data bus. Using all of the available data and internal
programming, the ASSYST microprocessor then calcu-
lates the estimated time and distance to the next
required engine oil maintenance interval. The ASSYST
uses the multi-function indicator LCD to display that
data and, when necessary, issues audible alerts to the
vehicle operator through the electronic tone generator
on the cluster circuit board.
See the owner’s manual in the vehicle glove box for
more information on the features, use, operation and
resetting procedures for the ASSYST maintenance
computer. Proper diagnosis and testing of the
ASSYST engine oil maintenance computer, the CAN
data bus and the electronic data bus message inputs
to the EMIC that are used by the ASSYST computer
for its calculations requires the use of a DRBIIIt
scan tool. Refer to the appropriate diagnostic infor-
mation.
VA INSTRUMENT CLUSTER 8J - 19
LOW OIL LEVEL INDICATOR (Continued)
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