J1850 Communications Network

The J1850 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.

The micro-processor based subsystems included on this network are:
^ Powertrain control
^ Climate control

The J1850 communication 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 J1850 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 a Diagnostic Trouble Code (DTC).

Purpose
The information within this system is designed to diagnose J1850 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 J1850 communication network include:

Powertrain control module
^ Located in the engine compartment on the passenger side of the dash panel.
^ A failure of the communication network to the powertrain control module may result in a no start condition.
^ If communication to the powertrain control module fails during diagnosis. Communication System Diagnostics

Electronic Automatic Temperature Control (EATC) Module.
^ Located on the A/C evaporator core housing on the passenger side of the vehicle.
^ Loss of communication to powertrain control module may result in degraded automatic temperature control.
^ If communication to the electronic automatic temperature control module is lost.