System Description And Functional Operation: Notes

The body system on the 2003 LH 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 it's 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 VEHICLE COMMUNICATION  section of this general information.

Always begin by reading the diagnostic trouble codes using the DRB. Next, look for the symptom in DIAGNOSTIC INFORMATION AND PROCEDURES . This will direct you to the specific test(s) that must be performed.