Turn Signal Indicators; Diagnosis And Testing - Turn Signal Indicator; Operation; Description - Jeep Wrangler 2001 Service Manual

8Js - 34 INSTRUMENT CLUSTER
TACHOMETER (Continued)
munications Interface (PCI) data bus. The tachome-
ter is an air core magnetic unit that receives battery
current on the instrument cluster electronic circuit
board through the fused ignition switch output (run-
start) circuit whenever the ignition switch is in the
On or Start positions. The cluster is programmed to
move the gauge needle back to the low end of the
scale after the ignition switch is turned to the Off
position. The instrument cluster electronic circuitry
controls the gauge needle position and provides the
following features:
• Engine Speed Message - Each time the cluster
receives an engine speed message from the PCM it
will calculate the correct engine speed reading and
position the gauge needle at that speed position on
the gauge scale. The cluster will receive a new
engine speed message and reposition the gauge
pointer accordingly about every 86 milliseconds. The
gauge needle will continue to be positioned at the
actual engine speed position on the gauge scale until
the ignition switch is turned to the Off position.
• Message Failure - If the cluster fails to receive
an engine speed message, it will hold the gauge nee-
dle at the last indication for about six seconds, or
until the ignition switch is turned to the Off position,
whichever occurs first. If a new engine speed mes-
sage is not received after about six seconds, the
gauge needle will return to the far left (low) end of
the scale.
• Actuator Test - Each time the cluster is put
through the actuator test, the gauge needle will be
swept to several calibration points on the gauge scale
in a prescribed sequence to confirm the functionality
of the gauge and the cluster control circuitry.
The PCM continually monitors the crankshaft posi-
tion sensor to determine the engine speed, then
sends the proper engine speed messages to the
instrument cluster. For further diagnosis of the
tachometer or the instrument cluster circuitry that
controls the gauge, (Refer to 8 - ELECTRICAL/IN-
STRUMENT CLUSTER - DIAGNOSIS AND TEST-
ING). For proper diagnosis of the crankshaft position
sensor, the PCM, the PCI data bus, or the message
inputs to the instrument cluster that control the
tachometer, a DRBIII scan tool is required. Refer to
the appropriate diagnostic information.

TURN SIGNAL INDICATORS

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 overlay, between the
speedometer and the tachometer. Each turn signal
2001 JEEP WRANGLER
indicator consists of a stencil-like cutout of the Inter-
national Control and Display Symbol icon for "Turn
Warning" in the opaque layer of the instrument clus-
ter overlay. The dark outer layer of the overlay pre-
vents these icons from being clearly visible when
they are not illuminated. A green lens behind each
cutout in the opaque layer of the cluster overlay
causes the indicator to appear in green through the
translucent outer layer of the overlay when it is illu-
minated from behind by a Light Emitting Diode
(LED) 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. These
indicators are controlled by two individual hard
wired inputs from the turn signal switch and hazard
warning switch circuitry of the left multi-function
switch to the cluster. Each turn signal indicator
Light Emitting Diode (LED) is grounded on the
instrument cluster electronic circuit board at all
times; therefore, the LED can be on anytime the turn
signal or hazard warning systems are turned on,
regardless of the ignition switch position. Each LED
will only illuminate when it is provided battery cur-
rent by the turn signal switch or hazard warning
switch circuitry of the left multi-function switch.
The turn signal switch and hazard warning switch
circuitry of the left multi-function switch are con-
nected in series between the output of the combina-
tion flasher on the left multi-function switch and the
left or right turn signal inputs to the instrument
cluster, but in parallel with the other turn signal cir-
cuits. This arrangement allows the turn signal indi-
cators to remain functional, regardless of the
condition of the other circuits in the turn signal and
hazard warning systems. The turn signal switch and
hazard warning switch inputs to the instrument clus-
ter can be diagnosed using conventional diagnostic
tools and methods. (Refer to 8 - ELECTRICAL/
LAMPS/LIGHTING
FUNCTION SWITCH - OPERATION) for more
information on the turn signal switch and hazard
warning switch.
DIAGNOSIS AND TESTING - TURN SIGNAL
INDICATOR
The diagnosis found here addresses an inoperative
turn signal indicator condition. If the problem being
diagnosed is related to inoperative turn signal or
hazard warning lamps, be certain to repair the turn
signal and hazard warning system before attempting
- EXTERIOR/LEFT MULTI-
TJ