Body Control Module: Description and Operation

SYSTEM DESCRIPTION AND FUNCTIONAL OPERATION
The body system on the 2000 PL 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 The Vehicle Communication of this general information.

AIRBAG SYSTEM
The Airbag Control Module (ACM) is bolted to the floor panel transmission tunnel rearward from the gear shift selector inside the vehicle. The ACM mounting bracket is welded to the tunnel and is not serviced with the ACM. 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 via the 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 preprogrammed decision algorithm in the ACM microprocessor determines when the deceleration rate as signaled by the sensor indicates an impact that 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. 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 system malfunction, Whenever the ignition key is turned to the "run" or "start" position, the MIC performs a lamp check by turning the airbag warning lamp on for 6 - 8 seconds. If the lamp turns 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.

Perform the WARNING LAMP OPEN 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 POTASSIUM 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. IN ADDITION, 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 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 its 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.

THE AIRBAG MODULE INFLATOR ASSEMBLY CONTAINS SODIUM AZIDE AND POTASSIUM 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. IN ADDITION, 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 ELECTRICITY. 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 INTERCHANGEABLE, 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 MOPAR PARTS CATALOG.

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 DRBIII (R). Refer to the Table of Contents and select the specific DTC's to be diagnosed. 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, diagnostic trouble codes are used as a diagnostic tool.

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.

Stored Codes
Airbag codes are automatically stored in the ACM's memory as soon as the malfunction is detected.

A "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.

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 "ON" 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,

INSTRUMENT CLUSTER
The instrument cluster for the PL body is sometimes referred to as a "Smart Cluster Control Module" (SCCM). This is because it does much more than the one used in previous years. Some of the new features are that it controls the courtesy lamps, it receives and sends messages to other modules via the PCI bus circuit, it controls all the instrument illumination and the chime is also an integral part of the cluster. The front turn signals are now wired through the cluster and then go to the front lamps. The reason being that the DRL module is built into the cluster if the cluster is so equipped.

For the domestic market there are 2 models, base and premium. The difference is that the premium cluster is equipped with a tachometer and a low fuel lamp.

One button is used to switch the display from trip to total mileage. Holding the button when the display is in the trip mode will reset the trip mileage. This button is also used to put the cluster in self diagnostic mode. To put in self diagnostic mode press the button down and then turn the ignition to the run position. The gauges will increment to selected stops and all indicators will light with the exception of the turn signals, high beam, and fog lamp indictors. The oil lamp will come on when the ignition is turned ON and the engine is OFF, and most of the indicators will also come on briefly for a bulb check when the ignition is turned from OFF to ON. All of the LED's are replaceable however the individual gauges are not and require complete replacement of the cluster if one or more gauges are inoperable.

In the event that the instrument cluster looses communication with all other modules on the PCI bus, the cluster will display "nobus" in the VF display. The VF display also displays "Door", "Cruise", "Trac" and odometer trip or total.

If the cluster does not detect voltage on the courtesy lamp circuit, the message "FUSE" will alternate with the odometer/trip odometer for 30 seconds after the ignition is turned ON and for 15 seconds after the vehicle is first moved. The lack of voltage can be due to the M1 Fused B(+) (IOD) fuse being open, a bad or missing courtesy lamp bulb, or a circuit problem.

REMOTE KEYLESS ENTRY MODULE
The Remote Keyless Entry module controls the Power Door Locks and the Vehicle Theft Security System (VTSS). It also wakes up the Instrument Cluster to turn on the illuminated entry when it senses a signal from the RKE transmitter. The module communicates with other modules via the PCI bus circuit.

The RKE module monitors the Airbag Control Module messages for the purpose of monitoring the deployment of the airbag. Upon receiving that message along with the verification that the ignition is ON and the vehicle speed is zero, it will provide the "enhanced accident response feature". This feature will cause the module to unlock all doors and the instrument cluster to turn the courtesy lamps ON.

The RKE module communicates with the Powertrain Control Module to receive vehicle speed information to activate the rolling door lock feature, receive the "okay to lock" message, to receive the vehicle information number and receive body style information. Two transmitters are supplied with the vehicle but a total of 4 can be programmed to the module. The horn chirp on vehicle lock command is customer programmable.

VEHICLE THEFT SECURITY SYSTEM
THE VTSS monitors the vehicle doors, hood and the ignition for unauthorized operation. Additionally, the decklid key cylinder is monitored for tampering, such as attempts to punch out the key cylinder. The alarm activates by sounding the horn, flashing the headlamps, park lamps and the VTSS indicator in the instrument cluster. Locking the doors with the door lock switch (through following a normal exit sequence of opening the door, pressing the lock button, and closing the door), the door cylinder lock switches or the RKE transmitter arms the system. During the 16 second arming process the VTSS indicator will flash quickly and when the system is armed will slow down. If the hood switch is grounded or the decklid security switch (knock-out) is not grounded, the LED will stay on steady during arming. The engine kill feature on domestic vehicles is accomplished via the Sentry Key Immobilizer Module (SKIM).

All of the sensors for the VTS system can be monitored using the DRBIII (R). The DRBIII (R) is also useful to determine the cause of a customer complaint of the alarm going off with no apparent reason.

POWER DOOR LOCKS
Central Locking
This feature allows the customer to lock/unlock all vehicle doors with the key from either front door lock cylinder switch. The customer can choose to program this feature to unlock all doors with one turn of the key or open the driver door only with the first turn of the key and open the other doors with the second turn. Altering the operation of the unlock function via the key cylinder switch from one turn to two turns will also alter the operation of the RKE transmitter from one press to two presses.

Rolling (Automatic) Door Locks
All vehicle doors are locked automatically once the vehicle reaches a speed of 15 mph and all doors are closed. This feature can be also be enabled/ disabled by the customer.

Door Lock Inhibit
This feature disables the door lock command from the interior door lock switch whenever the driver door is open and the key is in the ignition. This prevents the driver from locking the keys in the ignition when using the power door locks. This feature is inoperable if the IOD fuse is not installed.

Power Decklid Release
Electrically releases the decklid upon two presses of the RKE transmitter decklid release button. This feature is disabled once the speed of the vehicle is greater than 5 mph. This feature may be altered with the DRBIII (R) to allow the decklid to be released with one press of the RKE transmitter decklid release button.

Panic Mode
Upon activation of the panic function, the head-lamps and park lamps flash in an alternating manner, the horn pulses every second and the courtesy lamps are turned ON. The panic mode allows normal night time driving by allowing the headlamps and park lamps to be on steady when the headlamp switch is in the on position. Panic mode is activated immediately by pressing the panic button once. It does not disarm the VTSS or unlock the doors. It is canceled by pressing the button a second time, reaching a vehicle speed greater than 15 mph or after 3 minutes has elapsed in panic mode. Once panic mode has been activated there is a 2-second delay before it will turn OFF. Once it is cancelled there is a 2-second delay before it can be reactivated. This is to avoid the problem of deactivating and immediate reactivating due to multiple button presses.

SENTRY KEY IMMOBILIZER SYSTEM (SKIS)
The SKIS is an immobilizer system designed to prevent unauthorized vehicle operation. The system consists of a Sentry Key Immobilizer Module (SKIM) and ignition key(s) called Sentry Key(s) which are equipped with a transponder chip. The SKIM communicates over the Programmable Communication Interface multiplex system (PCI) bus network to the instrument cluster, Powertrain Control Module (PCM), and the DRBIII (R) scan tool.

The SKIM sends messages to the instrument cluster over the PCI bus to control the VTSS indicator lamp. The SKIM sends a message to the instrument cluster to turn the lamp ON for about three seconds when the ignition is turned to the Run/Start position as a bulb test. If the indicator lamp comes ON and stays ON after the bulb test, it indicates that the SKIM has detected a system malfunction and/or that the SKIS has become inoperative. If an invalid key is detected in the ignition key cylinder with the ignition switch in the Run Start position, the SKIM will flash the VTSS indicator lamp ON and OFF.

For additional information on the SKIS, refer to the Powertrain Diagnostic Procedures.




COMMUNICATION
The Programmable Communication Interface or PCI Bus is a single wire multiplexed network capable of supporting binary encoded messages shared between multiple modules. The PCI bus circuit is identified as D25 and is violet with a yellow tracer. The modules are wired in parallel. Connections are made in the harness using splices. The following modules are used on 2000 PL:
- Airbag Control Module
- Controller Antilock Brake
- Powertrain Control Module
- Remote Keyless Entry Module
- Sentry Key Immobilizer Module
- Mechanical Instrument Cluster

Each module provides its own bias and termination 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 averaging 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 DRBIII (R) lab scope. The 12 V 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 figure for some typical displays.

The PCI Bus failure modes are broken down into two categories. Complete PCI Bus Failure and individual module no response. Causes of Complete PCI Bus Failure include a short to ground or battery on the PCI circuit. Individual module no response can be caused by an open circuit at the module, or an open battery or ground circuit to the affected module.

Symptoms of a Complete PCI Bus Failure would include but are not limited to:
- All gauges on the MIC stay at zero
- All telltales on MIC illuminate
- MIC backlighting at full intensity
- No response received from any module on the PCI bus
- No start (if equipped with Sentry Key Immobilizer)

Symptoms of Individual module failure could include any one or more of the above. The difference would be that at least one or more modules would respond to the DRBIII (R).

Diagnosis starts with symptom identification. If Complete PCI Bus Failure is suspected, begin by identifying which modules the vehicle is equipped with and then attempt to get a response from the modules with the DRBIII (R). If any modules are responding, the failure is not related to the total bus, but can be caused by one or more modules PCI circuit or power supply and ground circuits. The DRBIII (R) may display "BUS + AND - OPEN" OR "NO RESPONSE" to indicate a communication problem. These same messages will be displayed if the vehicle is not equipped with that particular module. The CCD error message is a default message used by the DRBIII (R) and in no way indicates whether or not the PCI bus is operational. The message is only an indication that a module is either not responding or the vehicle is not equipped.