Perform Ring Break Test

WARNING: This page does not describe the selected car, but rather 59 other vehicles, including the 2009 BMW M5, 2009 BMW 650i, 2009 BMW 550i, 2008 BMW M5, and 2008 BMW 760Li. However, it is still accessible from the selected car via links, so may be relevant.

The ring break test mode is entered automatically when the power to all the modules in the MOST network is switched off and then switched back on. The most effective method of switching the power off and on is to disconnect the battery negative terminal for 45 seconds. This time will allow the capacitors of all the control modules to dissipate.

When the battery is reconnected the control modules wake up and in MOST network order transmit a light signal to the next module. Each module checks to see if it has received a light signal from the previous module. If the control module does NOT receive a light input signal it still transmits a signal to the next module. A relative node number of 0 is stored in the control module that did not receive a signal but that transmitted one.

The Control Display receives the light signal back and identifies which modules responded.

Go to "Control Unit Functions" Control Display Gateway and read fault memory.

The Control Display will display a relative node number. This number will indicate how many modules communicated after the module which set the relative node number of 0.

To find the control module with the relative node number of 0, count from the input side of the Control Display (counting the Control Display as 0) towards the control modules. When arriving at the control module with the number as displayed as the relative node number in the DISplus, the last known communicating module has been found.

Example:

While performing the ring break diagnostics the Control Display has set a relative node number of 2. Count the Control Display a 0, the Kombi will be 1 and the ASK will be 2.

The ring break occurs between the ASK and the module which precedes it, the telephone module.

IMPORTANT: When counting control modules, the multimedia changer (if equipped) and the Nav system must be counted as two control modules.

In order to perform the count correctly the equipment on the vehicle must first be identified.

When using the MOST network diagram in the DISplus, connector number 1 of the optical waves are inputs and connector number 2 are outputs.