Description of On-Board Diagnosis

SYSTEM DESCRIPTION AND FUNCTIONAL OPERATION
The body system consists of two modules that communicate over the CCD bus (Chrysler Collision Detection multiplex system). All of the information about the functioning of all the systems is organized, controlled, and communicated by the CCD bus.

Through the CCD 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 the wiring harnesses.

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 airbag control module (ACM) is an electronic module that monitors the airbag system for proper operation, stores diagnostic trouble code (DTC's), controls the airbag warning lamp, and contains the sensor and actuator that is responsible for airbag deployment. The ACM provides diagnostic information (DTC's) to the technician through the DRB Ill via the CCD bus. Some circuits are tested continuously; others are checked only under certain circumstances. The warning lamp is hard-wired to the ACM and there are no external impact sensors. The ACM is located in the center of the instrument panel under the heater control module.

The airbag warning lamp is the only point at which "symptoms" of a system malfunction can be observed by the customer. Whenever the ignition key is turned to the "run" or "start" position, the airbag control module 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 wire that operates the lamp may be 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 CIRCUIT OPEN test to find the cause of any customer complaint regarding the AIRBAG warning lamp, such as:
- warning lamp does not illuminate
- warning lamp stays illuminated

The deceleration or g-force resulting from the impact of a front-end collision causes the electronic sensor inside the ACM to be triggered. This causes the inflators to be actuated thus deploying the airbags. The total time between triggering to full deployment is usually 1/10 of a second.

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 code(s).

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 to diagnose an individual code.

Always begin by reading the diagnostic trouble codes using the DRB. This procedure begins with AIRBAG TEST 1A - Identifying Airbag System Problems. This will direct you to the specific test(s) that must be performed. If more than one code exists, diagnostic priority should be given to the active code(s).

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 and stored after one minute of occurrence 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 after one minute of occurrence or when the ignition is turned off. The exception is the "Loss of Ignition Run Only" code which is an active code only.

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 that 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

Airbag Trouble Codes
The airbag control module may report any of the following diagnostic trouble codes.

For the following codes, replace the airbag control module (ACM) even if set intermittently:
- AECM Accelerometer
- Internal Diagnostic 1
- Internal Diagnostic 2

For the following codes, replace the airbag control module (ACM).
- AECM Output Driver
- AECM Stored Energy Logic
- AECM Stored Energy Driver
- AECM Stored Energy Passenger
- Internal Diagnostic 3
- Internal Diagnostic 4
- Safing Sensor Shorted
- Warning Lamp Driver Error

For these codes, refer to Information Bus Diagnostic Charts:
- Driver Squib Circuit Open
- Driver Squib Circuit Shorted
- Loss of Ignition Run Only
- Loss of Ignition Run/Start
- No CCD Communication
- Passenger Squib Circuit Open
- Passenger Squib Circuit Shorted
- Either Squib Term Shorted to Battery
- Either Squib Term Short to Ground
- Warning Lamp Circuit Open
- Warning Lamp Circuit Shorted

ENTRY MODULE
The 1996 Viper Coupe utilizes a new Entry Module (EM). This system replaces the prior year Vehicle Theft Alarm and Remote Keyless Entry modules. The new module is located on the left side of the transmission tunnel, above the knee bolster. It is secured with a rubber strap. It contains a 32-way and two 6-way connectors. There is a green six way connector and a black six way connector. The module is connected to the CCD bus and transmits the "ok to run" message to the PCM when the theft alarm function is not tripped. It also receives the vehicle speed message from the bus. There is also a hard-wired backup circuit for vehicle speed.

The Entry Module provides remote keyless entry functions as well as vehicle theft alarm functions, electric locking/unlocking and the opening or power unlatching of the doors. The 1996 coupe utilizes power unlatching of the doors based only on inputs from the switches on the inside or the outside of the vehicle. The unlock button on the fob will not power unlatch the door. It also allows for the rolling lock feature, the only difference from other rolling lock systems is that specific throttle angle is not required for the locks to actuate. It is strictly a speed based system.

The Coupe will use new electric door latches to accomplish opening and closing of the vehicle doors and electronics to accomplish the lock function that was typically performed with linkage inside the door. The new system utilizes electric latches inside the door and switches both inside and outside the vehicle. These switches are inputs to the EM and if the conditions are correct, the EM will unlatch the door. The lock function is simply the ignoring of the switch inputs that would normally open the doors. There is no mechanical lock linkage inside the door. This results in fewer moving parts and problems associated with packaging the linkage mechanisms. The outside and inside door handles control micro switches that are the inputs to the EM. Located below the inside door switches are the lock rocker switches with LED indicators. The LED lock indicator informs the driver and passenger of the lock status of the doors. If the light is off, the doors are locked. Once the vehicle is started and driven approximately 8 mph (+/-3) the doors will automatically lock, therefore, the LED will be extinguished at this time. There is no defeat of the rolling lock feature. If there is no activity for approximately one minute (input to the EM) and the key is in the "on" or "off" position, the LED will be turned off to reduce battery draw.

The driver and passenger lock switches are wired in parallel and form one input to the EM. When the EM receives a lock input, both doors are locked. When an unlock signal is input to the EM, both doors are unlocked. If the key is on, and an inside door handle input is seen and vehicle speed is below 5 mph, both doors will be unlocked (and ultimately power unlatched). The lock switch is a momentary contact type switch and either switch will lock or unlock both doors. In case of an electrical failure that would render the EM system inoperable, there is an emergency mechanical release for the door located in the "B" pillar area of the door. This can be accessed through the Liftglass area. The only way to access the driver compartment of the vehicle once it is locked, (without setting off the alarm) is with the key fob. There is an exterior lock cylinder for the lift glass, that allows opening with the key. This cylinder is not equipped with a disarm function. If the Liftglass is opened with the key when the alarm is armed, it will set oft the alarm. There is a new Liftglass ajar switch that mounts on the left gas prop. When the Liftglass is opened, the outer shell of the gas prop allows a micro switch to close and the Liftglass ajar circuit is tied to ground. The EM monitors this circuit and knows the glass is open. If the Liftglass is broken, the prop will extend and trip the alarm. By utilizing a prop switch in this manner, the vehicle is protected against opening or breakage of the Liftglass.

The key fobs are unique to the Coupe and utilize a rolling code system. The rolling code feature changes the key fob message each time it is used. The key fob message and the receiver message increment together. Under certain conditions with a rolling code system, the receiver and transmitter can fall out of synchronization. By pressing the lock and unlock buttons together, the system will re-synchronize. The system will respond with a horn chirp and normal operation resumes. This is not the same as programming a key fob.

The system will accept up to four fob codes and the system can be programmed with either the DRB 111 or by connecting a programming wire to ground and placing the module in programming mode. If the system is set up for programming, all key fobs available for the vehicle must be programmed at the same time. When the module is placed in program mode, all the previous information from the transmitters is erased and no information is placed there until the system recognizes a valid key fob. Pressing both lock and unlock buttons on the key fob at the same time will cause the system to respond with a horn chirp after approximately ten seconds. Then any other transmitters may be programmed. There is a time out after approximately 60 seconds of inactivity (no further transmitter recognized). If the system times out, it will have to be returned to programming mode with either the DRB 111 or by disconnecting and re-connecting the green programming wire located near the module connectors. The DRAB "Theft Alarm Monitor Screen" contains information about how many fobs have been programmed. The horn chirp feature can not be disabled.

The security portion of the module performs typical security functions. The system can be actively armed by pressing the lock button on the fob. The system responds with a single horn chirp, if the message is from a valid (programmed) key fob. This information can also be accessed on the VTSS monitor screen with the DRB Ill. The system will passively arm if the ignition is turned off and the key is removed, the hood and lift glass are closed, a door is open, pressing the lock button on the door and closing the door. There is a 15 second arming period. The security LED will turn on during the arming process and the horn will chirp on completion of the arming process. The security LED will then flash at a 10% duty cycle. The system can only be disarmed with a programmed key fob.

When the alarm is tripped, the park lamps and the horn will flash indicating that the vehicle has been tampered with. The alarm can be tripped by opening doors, hood, Liftglass or turning the ignition on. Once tripped, the alarm will sound for 2.5 minutes. The park and tail lamps will flash for approximately 18 minutes. The PCM will not allow the engine to start. If the EM has been tripped and 18 minutes have passed, the horn will chirp 3 times upon unlocking with the key fob to alert the driver that a theft condition may have taken place. Normal disarming with the key fob will result in two short horn chirps.

Diagnostics
The EM system is fully addressable with DRB Ill and it is the recommended method for diagnosis. The EM system does not display any Diagnostic Trouble Codes. All of the input switches to the EM can be read with DRB under the I/O screen. The doors can be unlatched with the DRB under actuator tests. If the inputs are OK and the outputs can be cycled with the DRB, the problem is usually the Entry Module.

VEHICLE COMMUNICATION
The Chrysler Collision Detection multiplex system (CCD 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, and 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 roughly 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" located in the module that supplies bus bias or voltage. Along with the module that supplies bias, some modules provide termination. Bias is the voltage necessary to make the bus operational. At least one point of termination is necessary, some systems use more than one. Some modules are capable of biasing and terminating the bus by themselves. Termination in the circuitry (a 120 ohm resistor placed across the bus) is required to complete the voltage divider network and also provides some electromagnetic protection for the bus. Without termination, voltage on the bus goes to approximately 5 volts on one wire and 0 volts on the other wire.

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. If there is a problem, refer to the Vehicle Communications Bus Failure Messages

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.

CCD BUS CIRCUIT OPERATION
The CCD Bus is used for communication between the Vehicle Theft Alarm (VTA) module, scan tool, and the Powertrain Control Module (PCM).Circuit D1 is used for CCD (+) and circuit D2 is used for CCD (-).

The CCD Bus is both an input and output from the Vehicle Theft Security System (VTSS) module. Circuit D1 is used for CCD (+) and circuit D2 is used for CCD (-). These circuits are connected in with the data link connector and the Powertrain Control Module (PCM).