Instrument Cluster Self Test; Vehicle Communication - Jeep Wrangler TJ 2006 Diagnostic Manual

GENERAL INFORMATION
indicators are hardwired to the cluster and some
indicators are controlled by messages received on
the PCI Bus. The vehicle Chime function, Courtesy
Lamp Output, the Battery Saver function, and the
Rear Window Defogger timer are contained inter-
nally within the cluster. The cluster contains a
vacuum fluorescent (VF) display for the Odometer/
Trip function. The cluster VF will also display
P-codes and vehicle status messages. The cluster
has the ability to store DTCs, communicate on the
PCI Bus, display engine information, and display
certain inputs using the DRBIII . The cluster is
also able to perform a manual self-test. For com-
plete description and operation of the Instrument
Cluster, refer to the TJ Service Manual Instrument
Cluster section. For diagnostic procedures, refer to
the TJ Body Diagnostic Procedures Manual.

3.5.2 INSTRUMENT CLUSTER SELF TEST

The Instrument Cluster is capable of performing a
diagnostic self test. The self test is actuated by
depressing and holding the trip reset button while
turning the ignition from the off to the on position.
The self test can also be initiated using the DRBIII .
The self test will terminate if the tachometer is
greater than 300 RPM, the ignition is turned off, or
the test is complete. For diagnostic procedures, refer
to the TJ Body Diagnostic Procedures Manual.

3.6 VEHICLE COMMUNICATION

The Programmable Communication Interface or
PCI Bus is a single wire multiplexed network capa-
ble of supporting binary encoded messages shared
between multiple modules. The PCI bus circuit is
identified as D25 and is white with a violet tracer.
The modules are wired in parallel. Connections are
made in the harness using splices. The following
modules are used on 2006 Jeep Wrangler (TJ).
• Airbag Control Module
• Mechanical Instrument Cluster
• Radio
•
Powertrain Control Module (NGC)
• Sentry Key Immobilizer Module
• Satellite Radio Receiver
•
Controller Antilock Brake (Not on the PCI Bus.
Communication with the scan tool is established
thru the SCI Transmit circuit).
Each module provides its own bias and termina-
tion in order to transmit and receive messages. The
bus voltage is at zero volts when no modules are
transmitting and is pulled up to about seven and a
half volts when modules are transmitting.
The bus messages are transmitted at a rate aver-
aging 10800 bits per second. Since there is only
voltage present when the modules transmit and the
message length is only about 500 milliseconds, it is
ineffective to try and measure the bus activity with
a conventional voltmeter. The preferred method is to
use the DRBIII lab scope. The 12v square wave
selection on the 20-volt scale provides a good view of
the bus activity. Voltage on the bus should pulse
between zero and about seven and a half volts. Refer
to the following figure for some typical displays.
8