Easiest way to reset K-bus (when cluster fails) other than unplugging LCM

[ElectroDan]

Is there a quicker way to reset the K-bus than disconnecting/reconnecting the LCM?

I suspect I have a faulty stereo system.

Around once a week since buying my 4.8iS last year, the K-bus would crash, where the indicators stop showing on the cluster, can't control the stereo, CD-changer goes offline, etc. I'd been temporarily fixing this by unplugging the LCM, but it's a bit of a faff.

I had thought it was the LCM gone bad, but I sent this off and had it tested (and the common components that fail were replaced), and it had no faults show up. So, once that was refitted and the problem came back, I decided to leave the stereo turned off (the screen was on but orange light off and no sound coming out) for a month and the problem didn't occur again.

I've got a replacement BMW headunit on it's way, but the K-bus crashed again driving in today when listening to music, as I now have a bluetooth adapter connected in place of the CD auto-changer. Is there an easy way to reset the K-bus?


I've found the battery slowly drains if I don't disconnect/reconnect the LCM (or battery) to reset the K-bus, enough so that the car won't start the following day. A tad annoying! So I have to perform the reset fairly soon after it happens.

[ElectroDan]

Oddly, unplugging the LCM didn't cure the fault today, which is the first time that's been the case.

The only difference I could think of, is that I now have the BlueMusic bluetooth adapter fitted in-place of my CD autochanger. So I unplugged that, unplugged the LCM and plugged it back in, and the fault has gone.

Bluetooth Music Adapter BMW E46 E39 E38 E53 E85 for 3+6 CD Changer Connector 4251072613315 | eBay

So having the bluetooth adapter connected stopped the K-bus from resetting when the LCM was unplugged. One thing I didn't think of at the time, was to check whether my phone was connected via bluetooth and somehow keeping a connection alive?

My battery level is now low, so looks like I'll be taking the beast out for a drive during lunch to charge it back up

[CapeX5]

You need to find out where the parasitic drain on battery is coming from and go from there. Lot's of youtube on how to do that part.

[SirHiss]

Sounds like you're having similar problems to me!

Here's my thread.

https://xoutpost.com/bmw-sav-forums/...s-end-lcm.html

What is the K-bus?

[ElectroDan]

Originally Posted by SirHiss

Sounds like you're having similar problems to me!

Here's my thread.

https://xoutpost.com/bmw-sav-forums/...s-end-lcm.html

What is the K-bus?

This should help explain the K-bus:

https://www.bmwgm5.com/K-Bus_Troubleshooting.htm

I read your thread. Sounds like your K-bus is also crashing (I think it can get corrupt data from a component which causes the crash) which is causing your various light issues etc. Once you reset the K-bus (by disconnecting the battery for example), things should start working again, for a while. At least, that's what happens with my X5. I now suspect either the Nav unit in the boot has an intermittent fault, or wiring is damaged on the audio system somewhere. I swapped my front screen for one with no blemishes, so that's an improvement, but it still flickers on and off so whatever is causing that could be what's crashing the K-bus.

You could have a permanent fault though I guess, so even a reset doesn't get things working?

[ElectroDan]

Despite having my LCM 'repaired', it turns out it was still going faulty, but only after using the stereo daily for around a week.


Anyway, I bought another LCM (fortunately from the same year 4.8iS), fitted and coded this to my VIN, set the mileage to 0, and have been using this for a few weeks now without my instrument cluster crashing. Hooray!


I'm guessing my original LCM was water damaged at some point. The guy who refurbished it said it looked like it had evidence of water having gotten to it.