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.

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.

Terminating resistors 

The installation locations are listed below for the purposes of measuring the terminating resistor values.

• R56 
  • F CAN 
    • Vehicles with Dynamic Stability Control (DSC)

      1 resistor is in the DSC control unit

      1 resistor is in the DSC sensor (under the front-passenger seat)

  • PT-CAN 
    • 1 resistor is in the SZL control unit in the version with steering angle sensor (SZL: steering column switch cluster)

      1 resistor is in the EPS control unit (EPS: electro-mechanical power steering)

• E60, E61, E63, E64 
  • F CAN 
    • Vehicles with AS  (Active Steering)

      1 resistor is in the cumulative steering-angle sensor in the steering box.

      1 resistor is in the DSC sensor (under the front passenger seat).

    • Vehicles without AS  (Active Steering)

      1 resistor is in the DSC control unit (DSC: Dynamic Stability Control

      1 resistor is in the DSC sensor 2 (under the front-passenger seat; DSC sensor 1 is under the driver's seat).

  • PT-CAN 
    • 1 resistor is in the DSC control unit (DSC: dynamic stability control)
    • 1 resistor is in the SGM control unit (safety and gateway module)

      From 09/2005, this resistor is in the KGM control unit (body-gateway module)

• E65, E66 
  • PT-CAN 
    • 1 resistor is in the wiring harness at the front on the right spring strut dome.

      This resistor can be disconnected from the PT-CAN.

    • 1 resistor is in the wiring harness under the back seat.

      This resistor cannot be disconnected.

• E70 
  • F CAN 
    • 1 resistor is in the SZL control unit (SZL: steering column switch cluster)
    • 1 resistor is in the DSC control unit (DSC: Dynamic Stability Control)
  • FlexRay 

    If the vehicle is equipped with option 2VA "Adaptive Drive", the 4 damper satellites are connected to the VDM control unit via the FlexRay data bus.

    This option (special equipment) comprises 2 systems: Vertical dynamics management (VDM) and active roll stabilization (ARS: sales designation "Dynamic Drive").

    A damper satellite is fitted to each shock absorber.

    • Vehicles with "Adaptive Drive"

      1 resistor in each damper satellite of the vertical dynamic management system (VDM)

  • PT-CAN 
    • 1 resistor is in the DSC control unit (DSC: Dynamic Stability Control)
    • 1 resistor is in the EMF control unit (EMF: electromagnetic parking brake)
• E81, E87, E90, E91, E92, E93 
  • F CAN 

    Different terminating resistors are used depending on the motorization:

    • Vehicles with engine N4... (basic variant and High equipment)

      1 resistor is in the SZL control unit (SZL: steering column switch cluster)

    • Vehicles with engine M47, M57, N5... (basic variant and High equipment)

      1 resistor is in the DSC control unit (DSC: Dynamic Stability Control)

      1 resistor is in the SZL control unit (SZL: steering column switch cluster)

  • PT-CAN 

    Different terminating resistors are used depending on the motorization:

    • Vehicles with engine N4... (basic variant and High equipment)

      1 resistor is in the DSC control unit (DSC: Dynamic Stability Control)

      1 resistor is in the JBE control unit (JBE: junction box electronics)

    • Vehicles with engine M47, M57, N5... (basic variant and High equipment)

      1 resistor is in the DSC control unit (DSC: Dynamic Stability Control)

      1 resistor is in the EKP control unit (EKP: controlled fuel pump)