Computers/Controls - 'Loss of Comm' DTC Explanation

NUMBER: 08-025-05

GROUP: Electrical

DATE: May 13, 2005

SUBJECT:
Loss Of Communication Diagnostic Trouble Codes

MODELS:

2005 (HB) Durango

2005 (ND) Dakota

DISCUSSION

When diagnosing vehicles for Diagnostic Trouble Codes (DCT's) relating to loss of communication between electronic modules (Loss Of Comm) it is important to remember that communications between modules operating on the "Buss System" goes on continuously. When the vehicle is operating, modules are communicating, or talking to each other virtually all of the time. In a situation where a module is disconnected or inoperative, another module may need information from the module that is not operating. If the information is not available, a "Loss Of Comm" DTC will be set. This will happen any time the vehicle is operated with a module which is not operating. A "Loss Of Comm" DTC does not necessarily mean that a module is defective. Caution must be used in this situation. Situations are very common where a module may have been disconnected while a vehicle was being worked on, or a fuse feeding a module was blown or removed which will lead to modules not communicating and setting DTC's. An example would be a radio being removed and replaced. A DTC could be set and stored, even after the radio is installed. Another example would be the IOD fuse being disconnected. Several DTC's could be set and stored because the electrical feeds to various modules would be dead and nothing is wrong with any of the modules. A third example could be that a harness was disconnected which fed one or more of the modules. Whenever "Loss Of Comm" DTC's are encountered, it is always best to clear the DTC's and then check to see if the DTC's come back and are active. The "Loss Of Comm" DTC's should be disregarded unless they are active or repeatable.

POLICY:
Information Only

Disclaimer:
This bulletin is supplied as technical information only and is not an authorization for repair.