next requ ired en gin e oil ma int enan ce is an ticipated.
ASSYST also provides several audible indications
using the electr onic tone generat or on t he instrument
cluster cir cuit board to supplement these visua l dis-
plays.
The indications of t he ASSYST engine oi l mainte-
nance indica tor a re not visible when th e LCD is not
illuminated. When illuminat ed, the ASSYST indica-
tions appear as dark ch ara cters and icons silh ouett ed
aga inst a n amber field. When t he exterior lighting is
turned Off, the display is illuminat ed a t m aximum
brightness. When the ext erior lighting is turn ed On ,
the displa y illuminat ion level can be adjusted in con-
cert with the cluster gen eral illu mination lighting
using th e “+” (plus) and “"” (minus) multi-fu nction
indicator push buttons. The ASSYST engine oil ma in-
tena nce indica tor is serviced a s a unit wit h the
instr umen t cluster.
OPERATION
The ASSYST engine oil ma int enan ce indica tor
microprocessor u ses numerous criter ia besides time
and mileage to evaluat e vehicle mainten ance require-
ment s. Time da ta is taken from t he electron ic digita l
clock integr al to t he instr umen t cluster. Vehicle dis-
tance data is obtained from the Controller Ant ilock
Brake (CAB) over t he Con troller Area Network
(CAN) data bus. Coolant temper atu re, engine oil
temper ature, engine oil level, en gin e oil qualit y,
engine speed, and engine load da ta a re obtained fr om
the Engine Control Modu le (E CM) over the CAN
da ta bus. Using a ll of t he available data a nd inter nal
pr ogrammin g, th e ASSYST microprocessor then cal-
cula tes t he estim ated tim e and distan ce to the next
required en gin e oil maintenan ce interval. The
ASSYST uses the multi-funct ion indicator LCD to
display that data and, when necessary, issu es audible
aler ts to the vehicle oper ator through the electronic
tone generat or on the cluster circuit boar d.
See the owner ’s manual in the vehicle glove box for
more information on the fea tures, use, oper ation and
resett ing procedur es for t he ASSYST maint enan ce
computer. Proper diagn osis and test ing of t he
ASSYST engine oil ma intenan ce comput er, the CAN
da ta bu s an d th e electronic data bus message inputs
to the E MIC that a re used by the ASSYST computer
for its calcula tions requ ires th e u se of a diagnostic
sca n tool. Refer to th e appropriate diagnostic infor-
mation.
MALFUNCTION INDICATOR
LAM P (M I L)
DESCRIPTION
A Malfunct ion In dicator Lamp (MIL) is standard
equipm ent on all in st rument clusters. Th e MIL is
locat ed nea r th e lower edge of th e in st rumen t clu st er,
to the right of the multi-function indicator displa y.
The MIL consist s of the In ternational Cont rol and
Displa y Symbol icon for “Engine” imprinted within a
recta ngular cutout in the opaque la yer of the instr u-
ment clu st er overlay. Th e dark outer layer of the
overlay pr events t he in dicator from being clear ly vis-
ible when it i s not illuminat ed. An amber Light
Emitting Diode (LE D) behind the cutout in the
opa que layer of the overla y causes the icon to appear
silhouetted again st a n a mber field through the tran s-
lucen t outer layer of th e overlay wh en th e indica tor
is illum ina ted from behin d by the LED, which is sol-
dered on to the inst rument cluster elect ronic circuit
board. The MIL is ser viced as a unit with th e in st ru-
ment cluster.
OPERATION
The Malfu nction Indicator La mp (MIL) gives an
indication to th e vehicle operator when the En gine
Contr ol Module (ECM) has recorded a Dia gnostic
Trouble Code (DTC) for an On -Board Diagnostics II
(OBDII) emissions-related circuit or com pon ent m al-
function. The MIL is con trolled by a tr ansist or on th e
instr umen t clu st er circuit boa rd based u pon cluster
pr ogrammin g and electronic messa ges r eceived by
the cluster from the ECM over the Cont roller Area
Net work (CAN) da ta bus. The MIL Light Emit ting
Diode (LED) is completely controlled by the instr u-
ment cluster logic circuit, an d t hat logic will only
allow this indicator to opera te when the inst rument
cluster detect s tha t th e ign ition swit ch is in t he On
position . Ther efore, the LED will alwa ys be off wh en
the ignition swit ch is in any position except On . The
LED only illu min ates when it is pr ovided a path t o
ground by the instru ment cluster transistor. Th e
instr umen t clu st er will tu rn on the MIL for the fol-
lowing r easons:
• Bulb Test - Ea ch time the ignition switch is
turned to the On position the MIL is illumina ted as a
bulb test. The indicator will remain illu minated until
the engin e is sta rted, or unt il t he ign ition switch is
turned to t he Off position , whichever occurs first.
• MIL La m p -On Me s sa g e - Each time the clus-
ter receives a MIL lamp-on messa ge fr om the ECM,
the indicator will be illum ina ted. The indicator will
rema in illu minated until the detected fault is
repaired, or until the ignition switch is turned t o the
Off position, whichever occurs first. For more infor-
mation on th e E CM and t he DTC set and reset
pa ramet ers, (Refer to 25 - EMISSIONS CONTROL -
OPERATION).
• Co m mu ni c a t io n E rro r - If the cluster receives
no lamp-on or la mp-off messa ge from th e ECM, the
MIL is illu minated by t he instrument cluster. The
indicator rem ains contr olled and illuminat ed by the
cluster until a valid lamp-on or lamp-off messa ge is
received from t he ECM.
VA INSTRUMENT CLUSTER 8J - 21
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