CLUSTER ILLUMINATION
The EMIC has several illumination lamps that are
illuminated when the exterior lighting is turned on
with the headlamp switch. The illumination intensity
of these lamps is adjusted when the interior lighting
thumbwheel on the headlamp switch is rotated (down
to dim, up to brighten) to one of six available minor
detent positions. The EMIC monitors a resistor multiplexed
input from the headlamp switch on a dimmer
input circuit. In response to that input, the
EMIC electronic circuitry by converting a 12-volt
input it receives from a fuse in the Integrated Power
Module (IPM) on a hard wired panel lamps dimmer
switch signal circuit to a 12-volt Pulse Width Modulated
(PWM) output. The EMIC uses this PWM output
to power the cluster illumination lamps and the
VFD units on the EMIC circuit board, then provides
a synchronized PWM output on the various hard
wired fused panel lamps dimmer switch signal circuits
to control and synchronize the illumination
intensity of other incandescent illumination lamps in
the vehicle. The cluster illumination lamps are
grounded at all times.
The EMIC also sends electronic dimming level
messages over the PCI data bus to other electronic
modules in the vehicle to control and synchronize the
illumination intensity of their VFD units to that of
the EMIC VFD units. In addition, the thumbwheel
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INSTRUMENT CLUSTER (Continued)
on the headlamp switch has a Parade Mode position
to provide a parade mode. The EMIC monitors the
request for this mode from the headlamp switch,
then sends an electronic dimming level message over
the PCI data bus to illuminate all VFD units in the
vehicle at full (daytime) intensity for easier visibility
when driving in daylight with the exterior lighting
turned on.
The hard wired headlamp switch and EMIC panel
lamps dimmer inputs and outputs may be diagnosed
using conventional diagnostic methods. However,
proper testing of the PWM output of the EMIC and
the electronic dimming level messages sent by the
EMIC over the PCI data bus requires the use of a
DRBIIIt scan tool. Refer to the appropriate diagnostic
information.