Replace LCM? $400 crapshoot.

[KevinC]

So I took the new-to-me Z4MC in for some needed 10-yr maintenance - had the belts replaced (they were original), brake fluid (3 years) and power steering fluid (5 years). I also had the mechanic check out some sort of rubbing in one of the wheel wheels at full lock. Turned out the brake cooling duct on the driver's side had become dislodged, and some wiring was also loose and rubbing a bit (but not chafed/damaged thankfully). He tidied everything up. Inspection 1 was completed before I brought the car home from New Jersey, so now everything is totally current.

The remaining odd issue I have is that my instrument lights are somewhat dimmer than they should be, a fact I am certain of having owned a Z4MC previously from new for 8 years. The tech and I agreed that throwing a $400 LCM (Light Control Module, aka the headlight switch) at the issue seemed like a lousy gamble, but what else could it be? When I mess around covering up the light sensor on the switch, it usually behaves as it should, dimming the backlighting on the cluster, radio display, and climate controls. But it also sometimes instead goes full bright (where it should be all the time during the day when the headlight switch is in the off position), before returning to some half-assed brightness. When covered it should never go full bright, that's the opposite of what it should be doing.

So I strongly suspect that the LCM must be flaky. If it were a wiring issue or some other electrical problem, I wouldn't expect this behavior. It's driving me crazy because I can't see squat on the speedo in most daylight conditions - it's like looking down a dark sewer pipe, nothing visible there AT ALL. Even at full brightness it's a strain (not the best-designed cluster on the planet in the first place) but at least it's usable. I live in an area where the speed limits on the local 2-lane highways is tightly enforced, and I really need to see my speed and be vigilant.

So - what's the consensus? Would you go ahead and throw a new LCM in at $400, knowing you can't return the part if it doesn't cure anything? (since it's an electrical item). Or would you just suffer with it as is? Or does anyone have any other troubleshooting suggestions? I would really like to resolve this, and it would be worth the $400 to me - IF it solves the problem.

[Rekla]

If you need to know your speed, you can use your phone GPS, or install a P3 gauge. I wouldn't be of any help on troubleshooting the 'dim/bright' issue you've described. Please post if you diagnosed the root cause.

[RossBMWZseries]

This issue has came up a few times with some of us experiencing this self dimming cluster intermittently. First step, if you have a scanner, scan it for codes. Chances are you’ll get a code pointing to the LCM. Perhaps you should replace it but seeing the code pop up could give you a peace of mind before throwing out $400. Do you have any other symptoms AT ALL, like signals not displaying on dash or radio buttons not responding?

[KevinC]

Car was scanned yesterday, nothing came up related at all. No other symptoms, but it is all the dash illumination (radio display, climate controls, switch backlights) in unison, not just the cluster.

Most likely I'll just wait until I'm due for another service visit and then decide then whether or not I want to swap out the LCM.. finances at the time will probably be the determining factor. My gut tells me it must be the cause. I'll update this thread with any news, even if months away from now. Thanks for the input so far, and if anyone else wants to chime in, please do.

[Steeler]

Almost like the dimmer wheel on the LCM is dirty and not making good contact through its travel. Maybe try some electronic cleaner spray on it.

After all Aridzona = dust.

[KevinC]

Originally Posted by dbarton62

Almost like the dimmer wheel on the LCM is dirty and not making good contact through its travel. Maybe try some electronic cleaner spray on it.

After all Aridzona = dust.

Funny you mention that - my first Z4MC had this problem. The dimmer wheel was flaky and the illumination would jump wildly as it was scrolled. Had it replaced under warranty. No issue with the wheel on this one - max brightness is the problem. This car has only been in Arizona for 3 months, while my other resided in metro Phoenix its entire life until I sold it in 2015. Yes, VERY dusty up there. Down here where I am now, not so much.

[pungo]

I believe the LCM contains the odometer reading, so there's some process to copy the instrument cluster odometer value to the the new LCM. If not done properly, the mileage tamper light will come on. Maybe you already knew this.

[KevinC]

^^ Yep I was aware it will have to be coded.

[CFoote]

If it's all the instrumentation (not just the gauges) that this is happening to, I would say throw a LCM at it - I take it your dealer wouldn't be willing to return the LCM if it doesn't work?

I know this sound stupid, but your battery cables are good, battery voltage is good, and nothing changes if you rev the engine up (producing some more current from the alternator).

Chris

[KevinC]

Originally Posted by CFoote

I know this sound stupid, but your battery cables are good, battery voltage is good, and nothing changes if you rev the engine up (producing some more current from the alternator).

Yes everything else works as it should. I just put a battery in it right after I bought it in November - the original from 2008 was still there. Crazy.

I think I will throw an LCM at it eventually. I ASSume the part will be unreturnable due to being an electrical part.

[StickMon]

DIS would probably be able to tell you if the LCM has a problem.
I leave how to install and run DIS as an exercise for the student.

Edit: Just saw in another thread that you've had that fun experience.

[wohcrag]

Hey all , just wanted to chime in 2003 z4 3.0i. I bought a LCM off Ebay to help in troubleshooting a problem with instrument cluster lights and high beam indicator. I swapped out my original and no anti theft light ....yet. I'm planning to use dis on my laptop for additional issues but the cluster lights seem to be dimming properly now. My advice remove LCM first get exact part # and vin from doner .Ps LCM removal was pretty easy and cost me $40 off Ebay.


Update : Problem returned. I've been reading online and with out the proper tools ista d etc. I have to go with dbarton62 on this i think it may be the kbus grounds behind glove box causing my intermittent problems. See https://www.bmwgm5.com/K-Bus_Troubleshooting.htm

[KevinC]

$40? That's awesome. There was one for sale for $100 recently by a boneyard and I offered $50, the guy countered at $90 and I passed on it. Kinda wishing I would have grabbed it as they don't seem to turn up too often. Your experience makes me even more sure that the LCM is the cause of my dim panel lights. At some point I gotta address it, it's driving me crazy.

[RossBMWZseries]

Do you guys get the chime sound as if you leave the headlight switch on, turn off the car, and open the door? I get it sometimes and it doesn’t go off even when I lock the car. It’ll chime for 30 minutes or so. According to pelican parts, that could be a symptom of a bad LCM that needs replacement. At this point, only lights in my cluster are the air bag light and SES. Still have no radio or AC because of this issue

[Steeler]

Originally Posted by RossBMWZseries

Do you guys get the chime sound as if you leave the headlight switch on, turn off the car, and open the door? I get it sometimes and it doesn’t go off even when I lock the car. It’ll chime for 30 minutes or so. According to pelican parts, that could be a symptom of a bad LCM that needs replacement. At this point, only lights in my cluster are the air bag light and SES. Still have no radio or AC because of this issue

Ross, did you not get at your ground bar behind the glove box?
That was the root of all my electrical issues.

Edit, to clarify, the ground bar itself wasn't the cause, it was my solution, by disconnecting each ground wire until the affected electrics came back online.
Turned out the window anti trap system was shorted.

[KevinC]

Originally Posted by RossBMWZseries

Do you guys get the chime sound as if you leave the headlight switch on, turn off the car, and open the door?

Chime behavior is normal on mine.

ONE time while driving I was fiddling around covering the light sensor on the switch itself. Normally in my car it has zero effect (which is wrong right there - it should affect the lighting and should be easily visible in daylight by watching the odometer and how dim/bright it is). But this one time I could get it to adjust and get dimmer when covering it, then brighter when removing my finger. Then - back to it's "normal" behavior of not doing anything. This to me is a clear indication that the LCM is FUBAR. Also having owned another Z4MC previously that was working properly, I know for a fact that this thing is kablooey, it's just being sure it's the LCM that's at fault that is tricky.

[RossBMWZseries]

Originally Posted by dbarton62

Ross, did you not get at your ground bar behind the glove box?
That was the root of all my electrical issues.

Edit, to clarify, the ground bar itself wasn't the cause, it was my solution, by disconnecting each ground wire until the affected electrics came back online.
Turned out the window anti trap system was shorted.

I did but after reading what you just wrote, I may have misunderstood what you said in your thread and now I think I did it wrong. I didn't disconnect each ground wire. I'll try that this weekend. When you disconnected each wire, was this with the battery unplugged and then you plugged it back in to test each ground wire? Thanks Dave

Originally Posted by KevinC

Chime behavior is normal on mine.

ONE time while driving I was fiddling around covering the light sensor on the switch itself. Normally in my car it has zero effect (which is wrong right there - it should affect the lighting and should be easily visible in daylight by watching the odometer and how dim/bright it is). But this one time I could get it to adjust and get dimmer when covering it, then brighter when removing my finger. Then - back to it's "normal" behavior of not doing anything. This to me is a clear indication that the LCM is FUBAR. Also having owned another Z4MC previously that was working properly, I know for a fact that this thing is kablooey, it's just being sure it's the LCM that's at fault that is tricky.

I see. The chime should only beep when you're driving and don't have your seat belt on OR when you leave your key in the ignition on position 1 and open your door. It shouldn't chime when the key is removed, lights are off, and car is locked. That happens to mine sometimes so I'm starting to think it may be the LCM. There's a few LCM's on eBay going cheap.

[Steeler]

Originally Posted by RossBMWZseries

I did but after reading what you just wrote, I may have misunderstood what you said in your thread and now I think I did it wrong. I didn't disconnect each ground wire. I'll try that this weekend. When you disconnected each wire, was this with the battery unplugged and then you plugged it back in to test each ground wire? Thanks Dave




I see. The chime should only beep when you're driving and don't have your seat belt on OR when you leave your key in the ignition on position 1 and open your door. It shouldn't chime when the key is removed, lights are off, and car is locked. That happens to mine sometimes so I'm starting to think it may be the LCM. There's a few LCM's on eBay going cheap.

Ross, yes battery connected

[garz747]

I would really try some De Oxit available at radio shack. My wifes Audi cabrio was doing something funky with the turn signal stalk and this did the trick.. worth a try for $10 or so.

[wohcrag]

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


hope it helps

[KevinC]

The symptoms described in the K-bus video above don't match mine at all, but thanks for sharing that.

[KevinC]

Well, I sold my motorcycle recently and had some "extra" cash so I decided I wanted to go ahead and replace the LCM to try to resolve my dim dash. I was pretty confident this would be the fix, because of the reasons posted above. I bit hard and replaced with a NEW switch of the proper part number, which amazingly was in stock at the local dealer in Tucson.

Well - there might be a VERY slight improvement, but probably not even that. I'll know for sure after some more time in various ambient lighting conditions. The odometer still is very dim and unreadable in most daylight conditions, and that isn't right per my experience with my first Z4MC. So what's left? The cluster itself? But would something flaky about the cluster lighting also affect the dimming of the radio display (non-nav), because it also is too dim along with the cluster, and when it does brighten slightly, they both go up/down together, as I would expect them to - which seems to eliminate the cluster itself as the problem and point to something like the LCM, but apparently that's not it. Frustrated and out a bunch of cash. At least I can sell the "old" LCM and recoup some money as there is apparently nothing wrong with it. Sigh.