Minor electrical glitch-bad relay? - The Unofficial BMW M5 Messageboard (m5board.com)

gsfent · 9th June 2006, 00:20

OK, turn on lights, and dash lights (speedo and tach) don't work. HVAC work fine. Also, window switches not lit up. The strange part is, when you turn the light switch on, there is momentary light. That would lead me to believe it is not a fuse. Is there some type of relay to look for?
Regards,
Jerry

gsfent · 9th June 2006, 00:53

Quote:

Originally Posted by gsfent

OK, turn on lights, and dash lights (speedo and tach) don't work. HVAC work fine. Also, window switches not lit up. The strange part is, when you turn the light switch on, there is momentary light. That would lead me to believe it is not a fuse. Is there some type of relay to look for?
Regards,
Jerry

Hey, it's been 20 minutes and no response!!!

(j/k, saw a bunch of these today and couldn't resist

)
Regards,
Jerry

Tozzy · 9th June 2006, 02:31

Could be the LCM, Most of the light switches activate each function through the K-BUS (computer network throughout the car, K=Body)The switch sends some data Bits to the LCM to activate the corresponding lightbulbs.
You could try and remove the sidewall infont of the passenger door(under the glovebox) and move the Massive cable harness going to the LCM sitting in there. If the lights wake up there could be a bad soldering point in the LCM.

Tozzy · 9th June 2006, 02:33

2 hours and 11 minutes from your first post!
I am soo sorry

Tozzy · 9th June 2006, 02:58

Hmm, could not let this go, soo....

There are 3 connectors on the LCM, pin 1 on the white 15pin connector delivers the current to the PW switch lights and to the instrument cluster. This is where you would put a voltmeter to check if the LCM is delivering 12V to the lights.

Have you tried turning the light dimmer position? this should affect the AC lighting as well but with computers you never know

gsfent · 9th June 2006, 04:35

Quote:

Originally Posted by Tozzy

Hmm, could not let this go, soo....

There are 3 connectors on the LCM, pin 1 on the white 15pin connector delivers the current to the PW switch lights and to the instrument cluster. This is where you would put a voltmeter to check if the LCM is delivering 12V to the lights.

Have you tried turning the light dimmer position? this should affect the AC lighting as well but with computers you never know

Thanks. I did try the rheostat, HVAC lights worked/dimmed fine. I fiddled with it when I went to leave the office. I turned the light switch on and off, from park to headlight. The dash lights and window switch lights flickered just briefly. Then, I put the car in reverse, the lights popped a couple of times and then stayed on. I drove home, tried switching light switch position, all worked correctly. Only strange thing was V1 going off in driveway when I put the lights from off to parking. Car just got a clutch, any chance the backup light switch got jostled and somehow affected the dash and window switch lights??
Regards,
Jerry

Tozzy · 10th June 2006, 02:59

Hmm ,the backup circuit is completely different from the instrument lights, backup is connected directly to the DME. But the illuminated shifter might be connected to the same circuit as the instrument cluster(could not find it in the diagrams) and if that wire is shorted you might get some strange behaviours like you have. If the shitfer is removed during a clutch change they might have missed the lightcable and it got pulled hard causing a short or broken circuit. If the lights fail again, check if the gearshifter light goes out at the same time, if so thats probably where your problem is located.

best of luck
/Thomas

gsfent · 11th June 2006, 18:14

Quote:

Originally Posted by Tozzy

Hmm ,the backup circuit is completely different from the instrument lights, backup is connected directly to the DME. But the illuminated shifter might be connected to the same circuit as the instrument cluster(could not find it in the diagrams) and if that wire is shorted you might get some strange behaviours like you have. If the shitfer is removed during a clutch change they might have missed the lightcable and it got pulled hard causing a short or broken circuit. If the lights fail again, check if the gearshifter light goes out at the same time, if so thats probably where your problem is located.

best of luck
/Thomas

Thanks. It happened yesterday, today it is fine. Very intermittant, happens while driving, bumps don't seem to make a difference. I will look at the gearshift light the next time it happens. BTW, where is the LCM and how is it accessed?

Regards,
Jerry

Nabio · 12th June 2006, 01:33

The LCM is under/behind the glovebox. First pull that plastic trim out from under the glovebox, then open the glovebox and remove the tabs on the pivot deal. You may need to unscrew something too, just take a look under there and see what's not letting you take out the glovebox. Anyways, once the glovebox is out the LCM is that big old thing behind it with a bunch of wires coming out. Careful though, if you pull a harness out the alarm may activate.

Tozzy · 12th June 2006, 01:53

Sorry Nabio, but the "big box" behind the glovebox is not the LCM, the LCM is in the sidewall. It is fastened with one skrew at the bottom and when removed the LCM slides downward with some struggle, alot of wires that are fastened with a plastic ribbon to the sidewall. It is not neccessary to remove the glovebox to access the LCM but it is easier to remove the LCM then(Have tried both). The module behind the glovebox I believe is the DME/ECU unit, have not checked this though.

Here is a pic of mine while I was installing the towing electrics: