J1850 Communications Network

J1850 Communication Network

The J 1850 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 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 section 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 described in this section in the order presented.

Module Identification

Modules included on this J1850 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, refer to Communication Systems Diagnostics.

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 passive anti-theft system or communication to the module may result in a no start condition.
- if communication to the PATs module fails during diagnostics, see charts for No Communication testing.