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8J - 20
INSTRUMENT CLUSTER
MALFUNCTION INDICATOR
LAMP (MIL)
DESCRIPTION
A Malfunction Indicator Lamp (MIL) is standard
equipment on all instrument clusters. The MIL is
located near the lower edge of the instrument cluster, to
the right of the multi-function indicator display. The
MIL consists of the International Control and Display
Symbol icon for "Engine" imprinted within a rectangu-
lar cutout 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. An amber Light Emitting Diode (LED)
behind the cutout in the opaque layer of the overlay
causes the icon to appear silhouetted against an amber
field 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 elec-
tronic circuit board. The MIL is serviced as a unit with
the instrument cluster.
OPERATION
The Malfunction Indicator Lamp (MIL) gives an indi-
cation to the vehicle operator when the Engine Control
Module (ECM) has recorded a Diagnostic Trouble Code
(DTC) for an On-Board Diagnostics II (OBDII) emissions-
related circuit or component malfunction. The MIL is
controlled by a transistor on the instrument cluster cir-
cuit board based upon cluster programming and elec-
tronic messages received by the cluster from the ECM
over the Controller Area Network (CAN) data bus. The
MIL Light Emitting Diode (LED) is completely controlled
by the instrument 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 posi-
tion. 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 MIL for the following reasons:
• Bulb Test - Each time the ignition switch is
turned to the On position the MIL is illuminated as a
bulb test. The indicator will remain illuminated until
the engine is started, or until the ignition switch is
turned to the Off position, whichever occurs first.
• MIL Lamp-On Message - Each time the clus-
ter receives a MIL lamp-on message from the ECM,
the indicator will be illuminated. The indicator will
remain illuminated until the detected fault is
repaired, or until the ignition switch is turned to the
Off position, whichever occurs first. For more infor-
mation on the ECM and the DTC set and reset
parameters, (Refer to 25 - EMISSIONS CONTROL -
OPERATION).
• Communication Error - If the cluster receives
no lamp-on or lamp-off message from the ECM, the
MIL is illuminated by the instrument cluster. The
indicator remains controlled and illuminated by the
cluster until a valid lamp-on or lamp-off message is
received from the ECM.
The ECM continually monitors the fuel and emis-
sions system circuits and sensors to decide whether
the system is in good operating condition. The ECM
then sends the proper lamp-on or lamp-off messages
to the instrument cluster. If the instrument cluster
turns on the MIL after the bulb test, it may indicate
that a malfunction has occurred and that the fuel
and emissions systems may require service. For
proper diagnosis of the fuel and emissions systems,
the ECM, the CAN data bus, or the electronic mes-
sage inputs to the instrument cluster that control the
MIL, a DRBIII
scan tool is required. Refer to the
appropriate diagnostic information.
MULTI-FUNCTION INDICATOR
DESCRIPTION
A multi-function indicator is standard equipment on
all instrument clusters. The multi-function indicator is
located near the lower edge of the instrument cluster,
directly below the speedometer. The multi-function indi-
cator consists of a Liquid Crystal Display (LCD) unit
and four push button-controlled switches that are sol-
dered onto the instrument cluster electronic circuit
board. The LCD is visible through a large rectangular
cutout in the instrument cluster overlay, while the four
switch push buttons extend through a black plastic
switch bezel located on the cluster lens directly below
the LCD. The four multi-function indicator push buttons
allow the vehicle operator to configure and adjust sev-
eral of the display features. The buttons are labeled
from left to right: "mi" (miles) or "km" (kilometers), an
icon depicting an analog clock face (clock), " " (minus),
and "+" (plus).
The multi-function indicator LCD displays both
alpha-numeric characters and numerous icons to pro-
vide information to the vehicle operator. The indications
of the multi-function indicator are not visible when the
LCD is not illuminated. When illuminated the indica-
tions 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 " " (minus) multi-function indicator push
buttons. The multi-function indicator LCD unit and
push button switches are serviced as a unit with the
instrument cluster.
VA
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