Specifications
49
Testing Testing Bus Systems
z To check I and K Bus operation:
• Activate the 4-way flashers.
I and K buses are working if the flash indicators light up on the instrument cluster.
• Turn the radio on and adjust the volume using MFL or MID/BMBT.
I and K buses are working if the volume changes.
NOTE:
i The following procedure is for 540/740/X5 models using the High Instrument Cluster system
(digital display message center).
z To check M, I, and K Bus operation:
1. Press Recirculation using the multifunction steering wheel switch (MFL).
If the vents move to the recirculation position, then the M, I, and K buses are operational. The
Recirculation signal is sent via the MFL to the I Bus, to the instrument cluster (KOMBI), to the
K Bus, to IHKA, and finally to the M Bus (Figure 4-7). This also checks the IKE (gateway).
Figure 4-7 Bus systems on a High Instrument Cluster system
Lamp Control/Check (LM)
The LM transmits and receives status information concerning light operation. The LM transmits
bulb status to the check control module. It also communicates to the IKE when turn signal, high
beam, and fog light indicators need to be activated.
The Lamp Module (LM) for the E38 controls and monitors all the outside lights on the vehicle.
Various displays and switches are also illuminated by an LM function. The LM incorporates power
transistor output stages with internal protection circuits. This eliminates fuses and relays that are
found on earlier lamp control systems. The LM is usually located in the passenger side kick panel
behind the footwell speaker, which provides airflow across the external LM heatsink for cooling.
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