J1850 Communication 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.

Two micro-processor based subsystems are included on this network:
- Powertrain Control Module (PCM)
- Anti-lock Brake/Traction Control (ABS/TC) module

The 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 module fails internally.

Any of these conditions will be detected and reported by the off-board tester after completing the data link diagnostic test.

Purpose
The information given 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 RH 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, refer to Communication Systems Diagnostics. Component Tests and General Diagnostics

Anti-Lock Brake System/Traction Control (ABS/TC) Module:
- located under the battery tray in the lower LH side of the engine compartment.
- works in conjunction with powertrain control module to control traction.
- if communication to the anti-lock brake system/traction control (ABS/TC) module fails during diagnostics, diagnose Antilock Brake System or Traction Control no communication concerns.