Bus diagnosis: Notes

WARNING: This page is about a different car, the 2001 Saab 9-3. However, it is still accessible from the selected car via links, so may be relevant.

Fig 1: Bus Diagnosis Connection Diagram

Courtesy of SAAB-SCANIA OF AMERICA, INC.

In a bus system, it is necessary for all the units to be able to communicate with each other. For example, the engine cannot be started unless the engine management system can receive the immobilizer information sent by TWICE (not OBDII).

Bus faults can be caused by a bus lead breaking. This could result in one or more systems disappearing from the bus concerned (I or P), depending on where the break in the wiring harness occurred.

If a short circuit occurs in a bus lead, all systems will disappear from the bus concerned (I or P).

Note that if the I-bus is short circuited, DICE will be the only bus system apart from the diesel engine control module that can be contacted with the diagnostic tool.

In the event of a grounding or power supply fault in one or more systems, these systems will no longer be able to communicate.