Sentry Key Immobilizer System (Skis); Vehicle Communication - Chrysler 300M 1999 Manual

Customer programmable features are: Horn chirp, one or two press decklid release, programming
a new transmitter (using a previously programmed transmitter) and rolling door locks.
3.13

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 Body Control
Module (BCM), Powertrain Control Module (PCM), and/or the DRB scan tool.
The SKIM sends messages to the Body Control Module (BCM) over the PCI bus to control the
VTSS indicator lamp. The SKIM sends a message to the BCM 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 manual.
3.14

Vehicle Communication

The Chrysler Programmable Communication Interface multiplex system (PCI bus) consists of a
single wire. The Body Control Module (BCM) acts as a splice to connect each module and the
Data Link Connector (DLC) together. Each module is wired in parallel to the data bus through its
PCI chip set and uses its local ground as the bus reference. The wiring is a minimum 20 gage.
The PCI bus wire insulation color will be yellow with a violet tracer. An extra tracer color may be
added along with the violet to help distinguish between different node connections.
The bus is designed to handle a maximum number of nodes to meet all of the bus load and timing
requirements. The bus resistance and capacitance is designed to provide a maximum level of
filtering without distorting the bus symbols. This is why extra capacitance and resistance should
not be added to the PCI Data Bus circuitry.
In order for an electronic control module to communicate on the PCI data bus, the module must
have bus interface electronics consisting of a transmitter/receiver (or transceiver) and Logic
control, bus termination for loading and filtering the bus, and wiring which interconnects the
system.
Because of the unique coding scheme used in the PCI bus, each module is required to have logic
control. The data moving on the bus is called symbols. The interface logic performs the following
functions: encode and decodes binary data into symbols, synchronizes all bus symbol timing and
edges, controls the sending and receiving of messages, monitors for bus arbitration, monitors for
corrupted symbols due to noise and controls the transceiver.
The bus logic control also provides the transceiver with the information it needs to transmit
symbols on the bus. The transceiver controls the waveshaping of each symbol that it transmits by
using internal voltage controlled current drivers. When the bus transceiver is turned on, the bus
driver ramps up the voltage to the set range and maintains this voltage until the driver is turned
off, at which time the voltage is ramped back down to the low voltage, ground. The transceiver is
design to allow for arbitration between modules. If more than one module is trying to access the
PCI bus at one time, the code determines the message that has the higher priority, and is then
allowed to access the bus first.
The PCI bus requires a resistance and capacitance termination load to ground to operate.
Because each bus transceiver can only source current to the bus, the resistance load is required
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