General Information

SYSTEM DESCRIPTION AND FUNCTIONAL OPERATION
The body system on the 1999 Jeep Cherokee consists of five modules that communicate over the CCD bus (Chrysler Collision Detection multiplex system). There are two additional modules, the Powertrain Control Module (PCM) and the Transmission Control Module (TCM) that are not part of the body system, but do utilize the CCD bus for communication. The TCM also utilizes the bus for diagnostics. The PCM sends and receives messages on the CCD bus; however, diagnostics are performed through the Serial Communication Interface or SCI, the same as last year. All of the information about the functioning of all the systems is organized, controlled and communicated by the CCD bus.

Through the CCD 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 although a module may not require all information to perform its function. Each module 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.

When replacing a blown fuse, it is important to use only a fuse having the correct amperage rating. The use of a fuse with a rating other than indicated may result in a dangerous electrical system overload. If a properly rated fuse continues to blow, it indicates a problem in the circuit that must be corrected.

When replacing any bulbs, do not touch the new bulb with your fingers. Oil contamination will severely shorten bulb life. If the new bulb comes in contact with an oily surface, clean the bulb with rubbing alcohol.