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DR
TRANS TEMP INDICATOR (Continued)
data bus, or the electronic message inputs to the
instrument cluster that control the transmission
over-temperature indicator, a DRBIII
required. Refer to the appropriate diagnostic infor-
mation.
TURN SIGNAL INDICATOR
DESCRIPTION
Two turn signal indicators, one right and one left,
are standard equipment on all instrument clusters.
The turn signal indicators are located near the upper
edge of the instrument cluster, between the speedom-
eter and the tachometer. Each turn signal indicator
consists of a stencil-like cutout of the International
Control and Display Symbol icon for "Turn Warning"
in the opaque layer of the instrument cluster overlay.
The dark outer layer of the overlay prevents these
icons from being clearly visible when they are not
illuminated. A green Light Emitting Diode (LED)
behind each turn signal indicator cutout in the
opaque layer of the overlay causes the icon to appear
in green 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 turn
signal indicators are serviced as a unit with the
instrument cluster.
OPERATION
The turn signal indicators give an indication to the
vehicle operator that the turn signal (left or right
indicator flashing) or hazard warning (both left and
right indicators flashing) have been selected and are
operating. These indicators are controlled by transis-
tors on the instrument cluster electronic circuit board
based upon the cluster programming, a hard wired
multiplex input received by the cluster from the turn
signal and hazard warning switch circuitry of the
multi-function switch on the turn/hazard switch mux
circuit, and electronic messages received from the
Front Control Module (FCM) over the Programmable
Communications Interface (PCI) data bus. Each turn
signal indicator Light Emitting Diode (LED) is com-
pletely controlled by the instrument cluster logic cir-
cuit, and that logic will allow this indicator to
operate whenever the instrument cluster receives a
battery current input on the fused B(+) circuit.
Therefore, each LED can be illuminated regardless of
the ignition switch position. The LED only illumi-
nates when it is provided a path to ground by the
instrument cluster transistor. The instrument cluster
will turn on the turn signal indicators for the follow-
ing reasons:
• Turn Signal-On Input - Each time the cluster
detects a turn signal-on input from the turn signal
scan tool is
switch circuitry of the multi-function switch on the
turn/hazard switch mux circuit, the requested turn
signal lamps and turn signal indicator will be flashed
on and off, and an electromechanical relay soldered
onto the cluster electronic circuit board will produce
a clicking sound to emulate a conventional turn sig-
nal flasher. The turn signals and the turn signal
indicators continue to flash on and off until the clus-
ter receives a turn signal-off input from the multi-
function switch, or until the ignition switch is turned
to the Off position, whichever occurs first. The
instrument cluster also sends an electronic message
to the FCM over the PCI data bus, and the FCM
flashes the appropriate exterior turn signal lamps. If
the FCM detects an inoperative turn signal circuit, it
increases the flash rate for the remaining operative
turn signals and sends an electronic message to the
instrument cluster. The instrument cluster then
increases the flash rate of the turn signal indicator
and the clicking rate of the electromechanical relay
to provide an indication of the problem to the vehicle
operator.
• Hazard Warning-On Input - Each time the
cluster detects a hazard warning-on input from the
hazard warning switch circuitry of the multi-function
switch on the turn/hazard switch mux circuit, all of
the turn signal lamps and both turn signal indicators
will be flashed on and off, and an electromechanical
relay soldered onto the cluster electronic circuit
board will produce a clicking sound to emulate a con-
ventional hazard warning flasher. The turn signals
and the turn signal indicators continue to flash on
and off until the cluster receives a hazard warning-
off input from the multi-function switch. The instru-
ment cluster also sends an electronic message to the
FCM over the PCI data bus, and the FCM flashes all
of the exterior turn signal lamps. If the FCM detects
an inoperative turn signal circuit, it increases the
flash rate for the remaining operative turn signals
and sends an electronic message to the instrument
cluster. The instrument cluster then increases the
flash rate of both turn signal indicators and the click-
ing rate of the electromechanical relay to provide an
indication of the problem to the vehicle operator.
• Actuator Test - Each time the cluster is put
through the actuator test, the turn signal indicators
will be turned on, then off again during the bulb
check portion of the test to confirm the functionality
of each LED and the cluster control circuitry.
The instrument cluster continually monitors the
multi-function switch to determine the proper turn
signal and hazard warning system control. The
instrument cluster then sends the proper turn signal
and hazard warning flasher-on and flasher-off mes-
INSTRUMENT CLUSTER
8J - 39
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