Information Bus: Description and Operation

The standard corporate protocol (SCP) communication network provides:
^ the ability for module-to-module communication by sharing required inputs and outputs instead of each component having an input or output wired directly to or from each affected module.
^ a common link for communication to an off-board tester through the data link connector (DLC) located under the instrument panel to the right of the steering column.

Two micro-processor based subsystems are included on this network:
^ powertrain control
^ passive anti-theft

The communication link (or bus) between these subsystems and the DLC consist of an unshielded twisted pair of wires:
^ Circuit 914 T/O Bus+
^ Circuit 915 PK/LB Bus-

Fault Tolerance
The SCP communication network will remain operational in the event:
^ one circuit is severed.
^ one circuit is shorted to ground.
^ one circuit is shorted to battery positive voltage (B+).
^ a termination resistor is lost within a module.
^ one or more modules fail internally.

Any of these conditions will be detected and reported to the off-board tester during diagnostics in the form of fault codes.

Purpose
The information given is designed to diagnose SCP communication network concerns. These concerns may:
^ affect normal functional operations of the vehicle.
^ be directly related to customer concerns.
^ be undetectable except during diagnostics.

To properly diagnose a network concern, follow the diagnostic procedure in the order presented.

Module Identification
Modules included on this SCP communication network include:

Powertrain Control Module (PCM):
^ located in the passenger side of the dash panel.
^ a failure of the communication network to the PCM may result in a no start condition.
^ if communication to the PCM fails during diagnosis, Diagnostic Trouble Code Tests and Associated Procedures

Passive Anti-Theft System (PATS) Module:
^ located under the instrument panel to the left of the steering column.
^ works with PCM to enable or disable engine start function.
^ failure of the PATS or communication to the module may result in a no start condition.
^ if communication to the PATS module fails during diagnostics, Diagnostic Trouble Code Tests and Associated Procedures







Diagnostic Communication Network
The international standards organization (ISO) 9141 communication link:
^ consists of a single wire, Circuit 70 (LB/W).
^ provides a common link for communication to an off-board tester through the data link connector (DLC) located under the instrument panel to the right of the steering column.
^ does not allow module-to-module communications.

Two micro-processor based subsystems are included on this network:
^ air bag diagnostic monitor system
^ anti-lock brake system

Fault Tolerance
The ISO 9141 communication link will fail if any of the following occur:

^ Circuit 70 (LB/W) shorted to ground.
^ Circuit 70 (LB/W) shorted to battery positive voltage (B+).
^ the air bag diagnostic monitor loses power or ground supply.
^ a module failure shorts the ISO 9141 communication link internally.

Purpose
The information given is designed to diagnose 1SO 9141 communication link concerns. These concerns may:
^ affect normal functional operations of the vehicle.
^ be directly related to customer concerns.
^ be undetectable except during diagnostics.

To properly diagnose a link concern, follow the diagnostic procedure in the order presented.

Module Identification
Modules included on this ISO 9141 communication link include:

Air bag diagnostic monitor:
^ located behind the instrument panel on the tunnel of the floorpan.
^ if communication to the air bag diagnostic monitor fails,

Anti-lock brake control module:
^ located on the lower RH radiator support.
^ if communication to the Anti-lock Brake System (ABS) module fails, Diagnostic Trouble Code Tests and Associated Procedures