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SYSTEM DESCRIPTION
The body system on the 2001 JR consists of a combination of modules that communicate over the PCI bus (Programmable Communication Interface multiplex system). Through the PCI bus, information about the operation of vehicle components and circuits is relayed quickly to the appropriate module(s). All modules receive all the information transmitted on the bus even though a module may not require all information to perform its function. It will only respond to messages "addressed" to it through a binary coding process. This method of data transmission significantly reduces the complexity of the wiring in the vehicle and the size of wiring harnesses. All of the information about the functioning of all the systems is organized, controlled and communicated by the PCI bus, which is described in the Vehicle Communication of this General Information.

Always begin by reading the diagnostic trouble codes using the DRB III. Next, look for the symptom in the Diagnostic Information and Procedures of the Table of Contents. This will direct you to the specific tests(s) that must be performed.

Important Note:
If the Powertrain Control Module has been changed and the correct VIN and mileage have not been programmed, a DTC will be set in the Airbag module. In addition, if the vehicle is equipped with a Sentry Key Immobilizer Module (SKIM), Secret Key data must be updated to enable starting. Refer to 2001 JR Powertrain Diagnostics for more information. Erase codes in all modules.