Functions of bus system analysis

Bus system analysis is a test module that automatically executes the following steps:

Step 1: Identification of engine type 

Identifying the engine type is a prerequisite for bus system analysis, since: different engines generate different fault code memory entries for the same cause of fault.

Step 2: Read fault memories of all control units 

Step 3: Check fault memory entries for undervoltage 

If the vehicle has suffered an undervoltage, the undervoltage is the most likely cause of the bus failure. Bus system analysis checks whether a fault memory entry indicating undervoltage is present in at least 2 control units.

If no undervoltage can be detected, continue with step 4.

Step 4: Check how many fault memory entries were found 

If at least 1 fault memory entry is present, continue with step 5.

Step 5: Evaluation of fault memory entries and creation of a list of most probable fault causes 

Bus system analysis computes the 3 most probable fault causes.

The 3 most probable fault causes are given in a list.

The most probable fault cause is at the top of the list.

Message in the BMW diagnosis system
The fault causes detected are as follows:
[1] ** ** Cause of fault PT-CAN
[2] ** Cause of fault ZGM
[3] * Cause of fault...
[4] End test module
The more stars (maximum 5) are allocated to a component, the more reliable the result that the cause of the fault is to be found in the area of the component.

The stars in front of a cause of fault indicate how probable the cause of fault is. 5 stars denote the most likely cause of fault.

1 star is allocated to a cause of fault that has very low probability.

Step 6: Selection of the test module 

The BMW diagnosis system proposes a separate test plan for each of the 3 most probable fault causes.