NOTE: Before replacing the Powertrain Control Module (PCM) or Engine Control Module (ECM), be certain to
check the related component/circuit integrity for failures not detected due to a double fault in the circuit.
Most PCM/ECM driver/control circuit failures are caused by internal component failures (i.e. relays and sole-
noids) and shorted circuits (i.e. pull-ups, drivers, and switched circuits). These failures are difficult to detect
when a double fault has occurred and only one DTC has been set.

When a Powertrain Control Module (PCM) for a gasoline engine, or a Engine Control Module for a diesel engine
and the Sentry Key Immobilizer Module (SKIM) on vehicles equipped with the Sentry Key Immobilizer System
(SKIS) are replaced at the same time, perform the following steps in order:

1. Program the new PCM/ECM.

2. Program the new SKIM.

3. Replace all ignition keys and program them into the new SKIM.

PROGRAMMING THE PCM/ECM/SKIM

The SKIS Secret Key is an ID code that is unique to each SKIM. This code is programmed and stored in the SKIM,
the PCM/ECM, and each ignition key transponder chip. When the PCM/ECM or SKIM is replaced, it is necessary to
program the Secret Key into the new modules using a diagnostic scan tool. Follow the programming steps outlined
in the diagnostic scan tool menu for the module being replaced as appropriate.

NOTE: Be certain to enter the correct country code for the SKIM. If the incorrect country code is pro-
grammed into the SKIM, it cannot be changed and the SKIM must be replaced.

NOTE: If the PCM/ECM and the SKIM are replaced at the same time, all vehicle ignition keys will need to be
replaced and the new keys programmed into the new SKIM.

NOTE: Programming the PCM/ECM or SKIM is done using a diagnostic scan tool and a PIN to enter secure
access mode. If three attempts are made to enter secure access mode using an incorrect PIN, secure
access mode will be locked out for one hour. To exit this lockout mode, turn the ignition to the RUN posi-
tion for one hour then enter the correct PIN. (Ensure all accessories are turned OFF. Also monitor the bat-
tery state and connect a battery charger if necessary).

PROGRAMMING IGNITION KEYS TO THE SKIM

Each ignition key transponder also has a unique ID code that is assigned at the time the key is manufactured.
When a key is programmed into the SKIM, the transponder ID code is learned by the module and the transponder
acquires the unique Secret Key ID code from the SKIM. To program ignition keys into the SKIM, follow the pro-
gramming steps outlined in the diagnostic scan tool for “Program Ignition Keys or Key FOBs” under the “SKIM”
menu item.

NOTE: A maximum of eight keys can be learned to each SKIM. Once a key is learned to a SKIM, that key
has acquired the Secret Key for that SKIM and cannot be transferred to any other SKIM or vehicle.

If ignition key programming is unsuccessful, the scan tool will display one of the following error messages:

•

Programming Not Attempted - The scan tool attempts to read the programmed key status and there are no
keys programmed into SKIM memory.

•

Programming Key Failed (Possible Used Key From Wrong Vehicle) - SKIM is unable to program an igni-
tion key transponder due to one of the following:

− The ignition key transponder is faulty.
− The ignition key transponder is or has been already programmed to another vehicle.

•

8 Keys Already Learned, Programming Not Done - The SKIM transponder ID memory is full.

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•

Learned Key In Ignition - The ID for the ignition key transponder currently in the ignition lock cylinder is
already programmed into SKIM memory.

COMMUNICATION

DESCRIPTION

The DaimlerChrysler Programmable Communication Interface (PCI) data bus system is a single wire multiplex sys-
tem used for vehicle communications on many DaimlerChrysler Corporation vehicles. Multiplexing is a system that
enables the transmission of several messages over a single channel or circuit. All DaimlerChrysler vehicles use this
principle for communication between various microprocessor-based electronic control modules. The PCI data bus
exceeds the Society of Automotive Engineers (SAE) J1850 Standard for Class B Multiplexing.

Many of the electronic control modules in a vehicle require information from the same sensing device. In the past,
if information from one sensing device was required by several controllers, a wire from each controller needed to be
connected in parallel to that sensor. In addition, each controller utilizing analog sensors required an Analog/Digital
(A/D) converter in order to

read

these sensor inputs. Multiplexing reduces wire harness complexity, sensor current

loads and controller hardware because each sensing device is connected to only one controller, which reads and
distributes the sensor information to the other controllers over the data bus. Also, because each controller on the
data bus can access the controller sensor inputs to every other controller on the data bus, more function and fea-
ture capabilities are possible.

In addition to reducing wire harness complexity, component sensor current loads and controller hardware, multiplex-
ing offers a diagnostic advantage. A multiplex system allows the information flowing between controllers to be mon-
itored using a diagnostic scan tool. The DaimlerChrysler system allows an electronic control module to broadcast
message data out onto the bus where all other electronic control modules can

hear

the messages that are being

sent. When a module hears a message on the data bus that it requires, it relays that message to its microprocessor.
Each module ignores the messages on the data bus that are being sent to other electronic control modules.

OPERATION

Data exchange between modules is achieved by serial transmission of encoded data over a single wire broadcast
network. The wire colors used for the PCI data bus circuits are yellow with a violet tracer, or violet with a yellow
tracer, depending upon the application. The PCI data bus messages are carried over the bus in the form of Variable
Pulse Width Modulated (VPWM) signals. The PCI data bus speed is an average 10.4 Kilo-bits per second (Kbps).
By comparison, the prior two-wire Chrysler Collision Detection (CCD) data bus system is designed to run at 7.8125
Kbps.

The voltage network used to transmit messages requires biasing and termination. Each module on the PCI data bus
system provides its own biasing and termination. Each module (also referred to as a node) terminates the bus
through a terminating resistor and a terminating capacitor. There are two types of nodes on the bus. The dominant
node terminates the bus through a 1 KW resistor and a 3300 pF capacitor. The Powertrain Control Module (PCM)
is the only dominant node for the PCI data bus system. A standard node terminates the bus through an 11 KW
resistor and a 330 pF capacitor.

The modules bias the bus when transmitting a message. The PCI bus uses low and high voltage levels to generate
signals. Low voltage is around zero volts and the high voltage is about seven and one-half volts. The low and high
voltage levels are generated by means of variable-pulse width modulation to form signals of varying length. The
Variable Pulse Width Modulation (VPWM) used in PCI bus messaging is a method in which both the state of the
bus and the width of the pulse are used to encode bit information. A

zero

bit is defined as a short low pulse or a

long high pulse. A

one

bit is defined as a long low pulse or a short high pulse. A low (passive) state on the bus

does not necessarily mean a zero bit. It also depends upon pulse width. If the width is short, it stands for a zero bit.
If the width is long, it stands for a one bit. Similarly, a high (active) state does not necessarily mean a one bit. This
too depends upon pulse width. If the width is short, it stands for a one bit. If the width is long, it stands for a zero
bit.

In the case where there are successive zero or one data bits, both the state of the bus and the width of the pulse
are changed alternately. This encoding scheme is used for two reasons. First, this ensures that only one symbol per
transition and one transition per symbol exists. On each transition, every transmitting module must decode the sym-
bol on the bus and begin timing of the next symbol. Since timing of the next symbol begins with the last transition
detected on the bus, all of the modules are re-synchronized with each symbol. This ensures that there are no accu-
mulated timing errors during PCI data bus communication.

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The second reason for this encoding scheme is to guarantee that the zero bit is the dominant bit on the bus. When
two modules are transmitting simultaneously on the bus, there must be some form of arbitration to determine which
module will gain control. A data collision occurs when two modules are transmitting different messages at the same
time. When a module is transmitting on the bus, it is reading the bus at the same time to ensure message integrity.
When a collision is detected, the module that transmitted the one bit stops sending messages over the bus until the
bus becomes idle.

Each module is capable of transmitting and receiving data simultaneously. The typical PCI bus message has the
following four components:

•

Message Header - One to three bytes in length. The header contains information identifying the message type
and length, message priority, target module(s) and sending module.

•

Data Byte(s) - This is the actual message that is being sent.

•

Cyclic Redundancy Check (CRC) Byte - This byte is used to detect errors during a message transmission.

•

In-Frame Response (IFR) byte(s) - If a response is required from the target module(s), it can be sent during
this frame. This function is described in greater detail in the following paragraph.

The IFR consists of one or more bytes, which are transmitted during a message. If the sending module requires
information to be received immediately, the target module(s) can send data over the bus during the original mes-
sage. This allows the sending module to receive time-critical information without having to wait for the target module
to access the bus. After the IFR is received, the sending module broadcasts an End of Frame (EOF) message and
releases control of the bus.

The PCI data bus can be monitored using a diagnostic scan tool. It is possible, however, for the bus to pass all
diagnostic scan tool tests and still be faulty if the voltage parameters are all within the specified range and false
messages are being sent.

MODULE-ANTI-LOCK BRAKES

DESCRIPTION

The Antilock Brake Module (ABM) is mounted to the
Hydraulic Control Unit (HCU) and operates the ABS
system.

OPERATION

The ABM voltage source is through the ignition switch in the RUN position. The ABM contains a self check program
that illuminates the ABS warning light when a system fault is detected. Faults are stored in a diagnostic program
memory and are accessible with the DRB III scan tool. ABS faults remain in memory until cleared, or until after the
vehicle is started approximately 50 times. Stored faults are not erased if the battery is disconnected.

NOTE: If the ABM is being replaced with a new ABM is must be reprogrammed with the use of a DRB III.

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