Chrysler New Yorker. Manual - part 351

3.0

SYSTEM DESCRIPTION AND FUNCTIONAL OPERATION

The body system on the 1999 300M consists of a combination of modules that communicate over
the PCI bus (Programmable Communication Interface multiplex system). Through the PCI bus,
information about the operation of vehicle components and circuits is relayed quickly to the
appropriate module(s). All modules receive all the information transmitted on the bus even though
a module may not require all information to perform it’s function. It will only respond to messages

addressed

to it through a binary coding process. This method of data transmission significantly

reduces the complexity of the wiring in the vehicle and the size of wiring harnesses. All of the
information about the functioning of all the systems is organized, controlled, and communicated
by the PCI bus, which is described in Section 3.14 (Vehicle Communication) of this general
information.

3.1

Airbag System

The Airbag Control Module (ACM) is secured to a bracket on the floor panel transmission tunnel
below the instrument panel inside the vehicle. The ACM mounting bracket also serves as the
instrument panel center support. The ACM contains a microprocessor, the impact sensor, and
energy storage capacitor. The microprocessor contains the airbag system logic. The ACM system
logic includes On-Board Diagnostics (OBD) capability, and communicates with the instrument
cluster circuitry on the Programmable Communication Interface (PCI) data bus to control the
airbag indicator lamp. The microprocessor in the ACM monitors the impact sensor signal and the
airbag system electrical circuits to determine the system readiness. If the ACM detects a
monitored system fault, it sends messages to the instrument cluster on the PCI data bus to turn
on the airbag indicator lamp. A pre-programmed decision algorithm in the ACM microprocessor
determines when the deceleration rate is severe enough to require airbag system protection.
When the programmed conditions are met, the ACM sends an electrical signal to deploy the
airbag system components. The impact sensor is an accelerometer that senses the rate of vehicle
deceleration, which provides verification of the direction and severity of an impact. The impact
sensor is calibrated for the specific vehicle, and is only serviced as a unit with the ACM. The ACM
also contains an energy-storage capacitor. This capacitor stores enough electrical energy to
deploy the airbags, for one second following a battery disconnect or failure during an impact. The
purpose of the capacitor is to provide airbag system protection in a severe secondary impact if the
initial impact has damaged or disconnected the battery, but was not severe enough to deploy the
airbags.

THE AIRBAG SYSTEM IS A SENSITIVE, COMPLEX ELECTROMECHANICAL UNIT. BEFORE
ATTEMPTING TO DIAGNOSE OR SERVICE ANY AIRBAG SYSTEM OR RELATED STEERING
WHEEL, STEERING COLUMN, OR INSTRUMENT PANEL COMPONENTS YOU MUST FIRST
DISCONNECT AND ISOLATE THE BATTERY NEGATIVE (GROUND) CABLE. WAIT TWO
MINUTES FOR THE SYSTEM CAPACITOR TO DISCHARGE BEFORE FURTHER SYSTEM
SERVICE. THIS IS THE ONLY SURE WAY TO DISABLE THE AIRBAG SYSTEM. FAILURE TO
DO THIS COULD RESULT IN ACCIDENTAL AIRBAG DEPLOYMENT AND POSSIBLE
PERSONAL INJURY. NEVER STRIKE OR KICK THE AIRBAG CONTROL MODULE, AS IT
CAN DAMAGE THE IMPACT SENSOR OR AFFECT ITS CALIBRATION. IF AN AIRBAG
CONTROL MODULE IS ACCIDENTALLY DROPPED DURING SERVICE, THE MODULE MUST
BE SCRAPPED AND REPLACED WITH A NEW UNIT.

The airbag warning lamp is the only point at which the customer can observe

symptoms

of a

system malfunction. Whenever the ignition key is turned to the

run

start

position, the MIC

performs a lamp check by turning the AIRBAG warning lamp on for 6-8 seconds. If the lamp
remains off, it means that the ACM has checked the system and found it to be free of discernible
malfunctions. If the lamp remains on, there could be an active fault in the system or the MIC lamp
circuit may be internally shorted to ground. If the lamp comes on and stays on for a period longer
than 6-8 seconds then goes off, there is usually an intermittent problem in the system.

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Perform the WARNING LAMP BULB OR DRIVER procedure in this book to find the cause of any
customer complaint regarding the AIRBAG warning lamp, such as:

•

warning lamp does not illuminate

•

warning lamp stays illuminated with no active DTC’s

The ACM cannot be repaired or adjusted and, if damaged or faulty, it must be replaced.

Driver Airbag Module (DAB)

The airbag protective trim cover is the most visible part of the driver side airbag system. The
module is mounted directly to the steering wheel. Located under the trim cover are the horn
switch, the airbag cushion, and the airbag cushion supporting components. The airbag module
includes a housing to which the cushion and inflator are attached and sealed. The airbag module
cannot be repaired, and must be replaced if deployed or in any way damaged. The inflator
assembly is mounted to the back of the airbag module. The inflator seals the hole in the airbag
cushion so it can discharge the gas it produces directly into the cushion when supplied with the
proper electrical signal. The protective trim cover is fitted to the front of the airbag module and
forms a decorative cover in the center of the steering wheel. Upon airbag deployment, this cover
will split at a predetermined breakout line.

THE AIRBAG MODULE INFLATOR ASSEMBLY CONTAINS SODIUM AZIDE AND POTAS-
SIUM NITRATE. THESE MATERIALS ARE POISONOUS AND EXTREMELY FLAMMABLE.
CONTACT WITH ACID, WATER, OR HEAVY METALS MAY PRODUCE HARMFUL AND
IRRITATING GASES (SODIUM HYDROXIDE IS FORMED IN THE PRESENCE OF MOISTURE)
OR COMBUSTIBLE COMPOUNDS. DO NOT PUNCTURE, INCINERATE, OR BRING INTO
CONTACT WITH ELECTRICITY. DO NOT STORE AT TEMPERATURE EXCEEDING 93°C
(200°F).

Clockspring
The clockspring is mounted on the steering column behind the steering wheel. This assembly
consists of a plastic housing which contains a flat, ribbon-like, electrically conductive tape that
winds and unwinds with the steering wheel rotation. The clockspring is used to maintain a
continuous electrical circuit between the instrument panel wire harness and the driver side airbag
module, the horn switch, and the vehicle speed control switches on vehicles that are so equipped.
The clockspring must be properly centered when it is installed on the steering column following
any service removal, or it will be damaged. The clockspring cannot be repaired it must be
replaced.

Passenger Airbag Module (PAB)

The airbag door in the instrument panel top cover above the glove box is the most visible part of
the passenger side airbag system. Located under the airbag door is the airbag cushion and it’s
supporting components. The airbag module includes a housing to which the cushion and inflator
are attached and sealed. The airbag module cannot be repaired, and must be replaced if
deployed or in any way damaged. The inflator assembly is mounted to the back of the airbag
module. The inflator includes a small canister of highly compressed argon gas. The inflator seals
the hole in the airbag cushion so it can discharge the compressed gas it contains directly into the
cushion when supplied with the proper electrical signal. The airbag door has a living hinge at the
top, which is secured to the instrument panel top cover. The door also has predetermined
breakout lines concealed beneath its decorative cover. Upon airbag deployment, the airbag door
will split at the breakout lines and the door will pivot out of the way.

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THE PASSENGER AIRBAG MODULE CONTAINS ARGON GAS PRESSURIZED TO OVER
2500 PSI. DO NOT ATTEMPT TO DISMANTLE AN AIRBAG MODULE OR TAMPER WITH ITS
INFLATOR. DO NOT PUNCTURE, INCINERATE, OR BRING INTO CONTACT WITH ELEC-
TRICITY. DO NOT STORE AT TEMPERATURE EXCEEDING 93°C (200°F).

REPLACE AIRBAG SYSTEM COMPONENTS ONLY WITH PARTS SPECIFIED IN THE
CHRYSLER MOPAR PARTS CATALOG. SUBSTITUTE PARTS MAY APPEAR INTER-
CHANGEABLE, BUT INTERNAL DIFFERENCES MAY RESULT IN INFERIOR OCCUPANT
PROTECTION. THE FASTENERS, SCREWS, AND BOLTS ORIGINALLY USED FOR THE
AIRBAG SYSTEM COMPONENTS HAVE SPECIAL COATINGS AND ARE SPECIFICALLY
DESIGNED FOR THE AIRBAG SYSTEM. THEY MUST NEVER BE REPLACED WITH ANY
SUBSTITUTES. ANY TIME A NEW FASTENER IS NEEDED, REPLACE IT WITH THE
CORRECT FASTENERS PROVIDED IN THE SERVICE PACKAGE OR SPECIFIED IN THE
CHRYSLER MOPAR PARTS CATALOG.

3.1.1

Airbag Diagnostic Trouble Codes

Airbag diagnostic trouble codes consist of active and stored codes. If more than one code exists,
diagnostic priority should be given to the active codes.

Each diagnostic trouble code is diagnosed by following a specific testing procedure. The
diagnostic test procedures contain step-by-step instructions for determining the cause of the
trouble codes. It is not necessary to perform all of the tests in this book to diagnose an individual
code.

Always begin by reading the diagnostic trouble codes using the DRB. The procedure begins with
AIRBAG TEST 1A - Identifying Airbag System Problems. This will direct you to the specific test(s)
that must be performed.

Active diagnostic trouble codes for the airbag system are not permanent and will change the
moment the reason for the code is corrected. In certain test procedures within this manual,
diagnostic trouble codes are used as a diagnostic tool.

3.1.2

Active Codes

The code becomes active as soon as the malfunction is detected or key-off, whichever occurs
first. An active trouble code indicates an on-going malfunction. This means that the defect is
currently there every time the airbag control module checks that circuit/function. It is impossible
to erase an active code; active codes automatically erase by themselves when the reason for the
code has been corrected.

With the exception of the warning lamp trouble codes or malfunctions, when a malfunction is
detected, the airbag lamp remains lit for a minimum of 12 seconds or as long as the malfunction
is present.

3.1.3

Stored Codes

Airbag codes are automatically stored in the ACM’s memory as soon as the malfunction is
detected. The exception is the

Loss of Ignition Run Only

code which is an active code only.

stored

code indicates there was an active code present at some time. However, the code

currently may not be present as an active code, although another active code could be.

When a trouble code occurs, the airbag warning lamp illuminates for 12 seconds minimum (even
if the problem existed for less than 12 seconds). The code is stored, along with the time in minutes
it was active, and the number of times the ignition has been cycled since the problem was last
detected.

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The minimum time shown for any code will be one minute, even if the code was actually present
for less than one minute. Thus, the time shown for a code that was present for two minutes 13
seconds, for example, would be three minutes.

If a malfunction is detected a diagnostic trouble code is stored and will remain stored as long as
the malfunction exists. When and if the malfunction ceases to exist, an ignition cycle count will be
initiated for that code. If the ignition cycle count reaches 100 without a reoccurrence of the same
malfunction, the diagnostic trouble code is erased and that ignition cycle counter is reset to zero.
If the malfunction reoccurs before the count reaches 100, then the ignition cycle counter will be
reset and the diagnostic trouble code will continue to be a stored code.

If a malfunction is not active while performing a diagnostic test procedure, the active code
diagnostic test will not locate the source of the problem. In this case, the stored code can indicate
an area to inspect.

If no obvious problems are found, erase stored codes, and with the ignition

wiggle the wire

harness and connectors, rotate the steering wheel from stop to stop. Recheck for codes
periodically as you work through the system. This procedure may uncover a malfunction that is
difficult to locate.

3.2

Audio System

There are three radio systems available that communicate on the PCI bus. They are RBR, RBN,
and RAZ models. They use the bus for two reasons. First is to communicate trouble codes to the
body control module, the second is for use with the driver memory selection system. The radio
stores two sets of station presets and can be recalled by pressing the optional memory select
button (located on the drivers door). The RBR will have 6 speakers and a 120 watt external
amplifier. The RBN will have 7 speakers and a 240 watt external amplifier. The RAZ will have 9
speakers and a 320 watt external amplifier. Depending on the manufacturer, some systems have
a Front/Rear channel system and others have a Left/Right channel system.

3.3

Auto Headlamps

The headlamps and park/tail lamps will be activated by the BCM when the headlamp switch is in
the auto mode. To activate the auto headlamps the BCM requires that: (1) the headlamp switch
is in the ‘‘A’’ position, (2) the engine is running, and (3) the light level sensed through the sun load
sensor falls below the calibrated level.

3.4

Body Control Module

The body control module (BCM) supplies vehicle occupants with visual and audible information
and controls various vehicle functions. To provide and receive information, the module is
interfaced to the vehicle’s serial bus communications network (the Programmable Communica-
tion Interface or PCI bus). This network consists of the powertrain control module (PCM), the
memory heat seat/mirror module (MHSMM), sentry key immobilizer module (SKIM), the trans-
mission control module (TCM), the electro/mechanical instrument cluster (MIC), the radio, the
optional overhead travel information system (OTIS), airbag control module (ACM), optional
antilock brakes (ABS) and the optional automatic temperature control (ATC) display head. The
BCM is operational when battery power is supplied to the module, ignition switch power is needed
for ignition switched functions.

The body control module provides the following features:

Automatic headlamp and foglamp
A/C switch status / evaporator temperature status
BCM diagnostic support
Central lock and unlock (VTSS only)

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