position and within about two seconds check for con-
tinuity between the ABS warning indicator driver cir-
cuit cavity of the instrument panel wire harness
connector (Connector C2) for the instrument cluster
and a good ground. There should be continuity for
about two seconds after ignition On, and then an
open circuit. If OK, proceed to the diagnosis for the
ABS brake system. (Refer to 5 - BRAKES - DIAGNO-
SIS AND TESTING). If not OK, go to Step 2.
(2) Turn the ignition switch to the Off position.
Disconnect and isolate the battery negative cable.
Remove the Controller Antilock Brake (CAB) relay
from the Power Distribution Center (PDC). Check for
continuity between the ABS warning indicator driver
circuit cavity of the instrument panel wire harness
connector (Connector C2) for the instrument cluster
and a good ground. There should be no continuity. If
OK, go to Step 3. If not OK, repair the shorted ABS
warning indicator driver circuit between the instru-
ment cluster and the PDC as required.
(3) Check for continuity between the ABS warning
indicator driver circuit cavities of the instrument
panel wire harness connector (Connector C2) for the
instrument cluster and the CAB relay receptacle in
the PDC. There should be continuity. If OK, proceed
to the diagnosis for the ABS brake system. (Refer to
5 - BRAKES - DIAGNOSIS AND TESTING). If not
OK, repair the open ABS warning indicator driver
circuit between the instrument cluster and the PDC
as required.
AIRBAG INDICATOR
DESCRIPTION
An airbag indicator is standard equipment on all
instrument clusters (Fig. 8). However, the instrument
cluster can be programmed to disable this indicator
on vehicles that are not equipped with the airbag
system, which is not available in some markets. The
airbag indicator is located near the lower edge of the
instrument cluster, to the right of center. The airbag
indicator consists of a stencil-like cutout of the Inter-
national Control and Display Symbol icon for “Air-
bag” 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. A red Light Emitting Diode (LED)
behind the cutout in the opaque layer of the overlay
causes the icon to appear in red through the translu-
cent outer layer of the overlay when the indicator is
illuminated from behind by the LED, which is sol-
dered onto the instrument cluster electronic circuit
board. The airbag indicator is serviced as a unit with
the instrument cluster.
OPERATION
The airbag indicator gives an indication to the
vehicle operator when the airbag system is faulty or
inoperative. The airbag indicator is controlled by a
transistor on the instrument cluster circuit board
based upon cluster programming and electronic mes-
sages received by the cluster from the Airbag Control
Module (ACM) over the Programmable Communica-
tions Interface (PCI) data bus. The airbag indicator
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 receives a battery current input
on the fused ignition switch output (run-start) cir-
cuit. Therefore, the LED will always be off when the
ignition switch is in any position except On or Start.
The LED only illuminates when it is provided a path
to ground by the instrument cluster transistor. The
instrument cluster will turn on the airbag indicator
for the following reasons:
• Bulb Test - Each time the ignition switch is
turned to the On position the airbag indicator is illu-
minated for about seven seconds. The first two sec-
onds is the cluster bulb test function, and the
remainder is the ACM bulb test function.
• ACM Lamp-On Message - Each time the clus-
ter receives a lamp-on message from the ACM, the
airbag indicator will be illuminated. The indicator
remains illuminated for about twelve seconds or until
the cluster receives a lamp-off message from the
ACM, whichever is longer.
• Communication Error - If the cluster receives
no airbag messages for five consecutive seconds, the
airbag
indicator
is
illuminated.
The
indicator
remains illuminated until the cluster receives a sin-
gle lamp-off message from the ACM.
• Actuator Test - Each time the cluster is put
through the actuator test, the airbag indicator will be
turned on, then off again during the bulb check por-
tion of the test to confirm the functionality of the
LED and the cluster control circuitry. The actuator
test illumination of the airbag indicator is a function
of the ACM.
The ACM continually monitors the airbag system
circuits and sensors to decide whether the system is
in good operating condition. The ACM then sends the
proper lamp-on or lamp-off messages to the instru-
ment cluster. If the ACM sends a lamp-on message
after the bulb test, it indicates that the ACM has
detected a system malfunction and/or that the air-
bags may not deploy when required, or may deploy
Fig. 8 Airbag Indicator
TJ
INSTRUMENT CLUSTER
8J - 21
ABS INDICATOR (Continued)