Information Bus: Description and Operation

CCD BUS
Also called Chrysler Collision Detection (CCD) Bus. Several systems communicate with each other using the CCD Bus.

The Chrysler Collision Detection multiplex system (CCD or Information bus) consists of a twisted pair of wires. These wires run from one module to another. They receive and deliver coded information between the modules. The information is coded to identify the message as well as the importance of the message. When there are multiple messages trying to access the CCD bus at one time, the code determines the message that has higher priority, which is then allowed to access the bus first.

The two wires of the twisted pair that make up the CCD multiplex system are called "bus(+)" (bus plus) and "bus(-)" (bus minus) respectively. Each wire has a measurable voltage level of approximately 2.5 volts. In order to maintain the 2.5 volts on each line and provide a means of transportation for the coded messages, there is a "voltage divider network". This network consists of the Instrument Cluster module which supplies bias and the PCM which supplies termination. Bias is the part of the voltage divider network that places both bus(+) and bus(-) at 2.5 volts. Termination in the circuitry is required to complete the voltage divider network and also provides some electromagnetic protection for the bus.

NOTE: Communication over the bus is essential to the proper operation of the vehicle's on-board diagnostic systems and the DRB. Problems with the operation of the bus or DRB must be corrected before proceeding with diagnostic testing.

Bus Failure Messages
- Short to Battery - Either or both of the bus wires are shorted to the battery potential.
- Short to 5 Volts - Either or both of the bus wires are shorted to a 5-volt potential.
- Short to Ground- Either or both of the bus wires are shorted to ground
- Bus (+) & Bus (-) Shorted Together - The two bus wires are shorted together.
- No Termination - The bus system has lost connection with its terminator.
- Bus Bias Level Too Low - Either or both of the bus wire potentials are significantly below their normal 2.5 volts.
- Bus Bias Level Too High - Either or both of the bus wire potentials are significantly above their normal 2.5 volts.
- No Bus Bias - The bus system has lost connection with the VTSS module which provides bias.
- Bus (+) Open - The bus (+) wire has lost connection with termination and/or bias.
- Bus (-) Open - The bus (-) wire has lost connection with termination and/or bias.
- Not Receiving Bus Messages Correctly - The DRB cannot communicate over the bus and does not know why.

AIRBAG SYSTEM
The airbag system is designed to provide increased driver and passenger protection if the vehicle is involved in a front-end collision. The system is most effective when used in conjunction with the seat belt system. The ACM is an electronically-triggered system that uses only its own internal electronic sensor to trigger the airbags.

Whenever the ignition key is turned to the "run" or "start" position, the airbag control module (ACM) performs a lamp check by turning the AIRBAG warning lamp on. The lamp stays lit for 6 to 8 seconds, then goes off. If the lamp remains oft, it means that the ACM has checked the system and found it to be free of discernible malfunctions. The airbag system is monitored by the ACM.

The ACM monitors critical input and output circuits within the airbag system, making sure they are operating correctly. Some circuits are tested continuously; others are checked only under certain circumstances. The ACM provides diagnostic information about the airbag system to the technician through the DRB via the CCD bus.

The AIRBAG warning lamp is the only point at which "symptoms" of a system malfunction can be observed by the customer. The seat belt warning lamp is used as a back-up for a failed airbag warning lamp. If at "ignition on" (when the airbag warning lamp should be activated for 7 seconds) the airbag lamp fails to come on for the 7 second bulb-check, the seat belt warning lamp will flash on and off for 30 seconds after its 7 second bulb-check and will perform as the airbag warning lamp.

The deceleration or g-force resulting from the impact of a front-end collision causes the electronic sensor inside of the ACM to be triggered. This causes the inflators to be actuated, thus deploying the airbags. The total time between determining to deploy and deflation of the airbag is 1/10th of a second.

Use the Powertrain Management/Computers and Control Systems/Information Bus test procedures to find the cause of any customer complaint regarding the AIRBAG warning lamp, such as:
- Warning lamp does not come on at all
- Warning lamp stays on

INSTRUMENT CLUSTER
The instrument cluster contains six gauges and eleven warning lamps. The gauges are positioned with information received by the cluster over the CCD bus from the PCM. Some of the lamps are hard-wired and some are controlled by the cluster using CCD bus information. The vehicle chime function is contained on the cluster circuit board as well as the timer for the rear window defogger. There is a self test available for the cluster that will actuate all the gauges and place them at their calibration points. The test will not run if the cluster sees engine RPM or vehicle speed. This test will light all CCD controlled lamps for verification of lamp operation. It also forces the odometer vacuum fluorescent display (VF) to count up from zero through nine. The self test routine can be entered by pushing and holding the trip reset button while rotating the ignition key from the "off" to the "on" position.

The VF display is also capable of displaying PCM DTCs in a numeric fashion rather than blinking the malfunction indicator lamp (MIL). This feature is accessed the same as in previous years by turning the key from off to run 3 times and staying in the run position.

The cluster will provide bus bias and the engine controller provides termination. If either of these components are disconnected the bus will not be operational.

The cluster will be serviced as an assembly. There will be limited parts available, bulbs and sockets, the front lens, the trip odometer stem cover and the rear cover assembly. No internal parts of the cluster will be serviced.

Normal Operation: At key on, the cluster will light the low fuel, seat belt, check gauges, airbag and upshift lamps (if equipped). As the key is turned farther towards the start position, the ABS (if equipped) and brake warning lamp will illuminate. The vacuum fluorescent (VF) display will indicate the mileage stored inside the cluster. If there is a bus failure and the cluster cannot receive distance pulses from the PCM the cluster will display the last mileage stored until the ignition is turned off. If the cluster is receiving bus messages but is unable to display odometer information because of an internal failure, the odometer will display dashes. VF dimming is handled by the potentiometer that controls instrumentation illumination.

HEATER REAR WINDOW DEFOGGER
The timing circuit for the rear window defogger is contained in the cluster. The operation is as follows: With ignition on, the first push of the defogger button will start a 10 minute timer. After 10 minutes have elapsed, the defogger will be turned off. If the button is pushed a second time during the same ignition cycle, the timer will turn the defogger on for 5 minutes. Every consecutive push will operate the defogger for 5 minutes. When the defogger is on, it can be turned off with a second push of the defogger button.

CHIME
The chime function is a 1000 Hz tone contained within the cluster. The cluster will not generate more than one chime per condition in the same ignition cycle. If a problem occurs that requires a second chime while the first one is currently being generated, the second chime request will be ignored. The chime will sound for the following conditions:
- Seat Belt Warning - 6 seconds after key on
- Key in Ignition Warning - door open with key in ignition
- Engine Temp High - when gauge enters red zone
- Engine Temp Critical - when gauge reaches the high end of the red zone
- Oil Pressure Low - below 6 psi and above 300 RPM
- Volt Gauge Low - when engine controller sets the "charge fail" DTC.
- Volt Gauge High - when engine controller sets the "voltage high" DTC.

LAMPS (HARD-WIRED)
The following lamps are hard-wired in the cluster and are not part of the self-test.
- Full Time 4WD (export only)
- Part Time 4WD
- Brake WARNING (red)
- ABS (amber)
- High Beam
- Left Turn Signal
- Right Turn signal
- Master Illumination (export only)

LAMPS (CCD)
The following lamps are controlled by the cluster via CCD messages. They are actuated during the self-test procedure.
- Low Fuel Warning
- Airbag
- Seat Belt
- Upshift (if equipped)
- Check Engine
- Check Gauges

GLOSSARY OF TERMS
ACM - Airbag Control Module
AECM - Airbag Electronic Control Module
Airbag Module - also called "Squib" Initiator. It is located inside the driver side Airbag Module assembly.
ASDM - Airbag System Diagnostic System
CCD - Chrysler Collision Detection (Vehicle Communication Bus)
DAB - Driver Airbag
PAB - Passenger Airbag
DLC - Data Link Connector
PCM - Powertrain Control Module
PDC - Power Distribution Center

CIRCUIT OPERATION
Circuits D1 and D2 connect the Powertrain Control Module (PCM) to the CCD Bus. Circuit D1 connects to cavity C30 of the PCM. Circuit D2 connects to cavity C28 of the PCM. Circuits D1 and D2 are a twisted pair of wires.

Several controllers and modules broadcast and receive data on the CCD Bus. Each controller or module is enabled to receive only certain messages. The PCM broadcasts the following messages on the CCD bus.
- Engine RPM
- Injector on-time and distance pulses
- Vehicle speed
- Engine oil pressure
- Engine temperature
- Fuel level
- System voltage