Town Car V8-4.6L (2008)
Network Topology (Part 2)
International Standards Organization (ISO) 9141 Network Operation
The ISO 9141 communications network is a single wire network, used for diagnostic purposes only.
The ISO 9141 communications network is used for the following modules:
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Liftgate/trunk module (LTM)
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Parking aid module (PAM)
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Restraints control module (RCM)
Standard Corporate Protocol (SCP) Communication Network
The SCP network has an unshielded twisted pair cable, data bus (+) and data bus (-) circuits. In addition to scan tool communication, this network
allows sharing of information between all modules on the network.
The SCP communication network is used for the following modules:
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Driver door module (DDM)
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Driver seat module (DSM)
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HVAC module
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Instrument cluster (IC)
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Lighting control module (LCM)
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Rear audio and temperature control (RATC) module
High Speed Controller Area Network (HS-CAN) Operation
The HS-CAN uses an unshielded twisted pair cable, data bus (+) and data bus (-) circuits. In addition to scan tool communication, this network allows
sharing of information between all modules on the network.
The HS-CAN is a high speed communication network used for the following modules:
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ABS module
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Vehicle dynamics module (VDM)
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Instrument cluster (IC)
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PCM
Network Termination
The CAN uses a network termination circuit to improve communication reliability. The network termination of the CAN bus takes place inside the
termination modules (ABS module and IC) by termination resistors. Termination modules are located at either end of the bus network. As network
messages are broadcast, in the form of voltage signals, the network voltage signals are stabilized by the termination resistors. Each termination module
has a 120 ohm resistor across the positive and negative bus connection in the termination module. With two termination modules on each network,
and the 120 ohm resistors located in a parallel circuit configuration, the total network impedance, or total resistance is 60 ohms.
Network termination improves bus message reliability by:
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stabilizing bus voltage.
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eliminating electrical interference.
Gateway Module
The IC is the gateway module, translating HS-CAN to SCP and vice versa. This information allows a message to be distributed throughout both
networks. The IC is the only module on this vehicle that has this ability.
