Variable sliding tach does not work properly..

[Rat3d ///M]

..and I am hoping to get some help in here, because this issue is driving me insane.

I know this will be long, but bear with me. I really need some help on this.

Basically what the car is doing, is the variable redline that goes around the tach does not reflect what the actual redline is. It will move to a certain point when you start the car, and stay there. It is 100% random where it moves to as well. Sometimes it will move to 6500 RPMs, sometimes it will move to 2300 RPMs, sometimes it will move to 8400 RPMs (even on a cold engine). No rhyme or reason for the insanity, and once it moves to wherever it decided to move to, it stays there. It does not change at all during the drive. Again, the indicated redline is not the actual redline. You can redline past wherever it may be all day.

So, I took the cluster out of the car, and took it apart to try and see if I could get it to work. I saw nothing that appeared to be broken, or that would indicate it as being faulty. I did however learn that the way it works, is there is a potentiometer (at least I think that's what it is, I am not an electronics expert?) soldered into the circuit board on the cluster. This POT has a gear on the end of it, which moves the redline "ring" around the tachometer. The cruise control indicator around the speedo side works the same exact way. Pretty simple it seems.

I played around with the cluster, moving the redline indicator around, and spinning the gear on the POT to ensure it wasn't sticking or anything. I took the circuit board (with no cluster casing, glass front, or gauge needles on it) and plugged it into the car so I could have access to the moving parts while it was in the car. I started the car, and I could tell that the variable redline wanted to work properly. It was moving upwards slightly (toward the 8400RPM mark) but seemed as though it was getting "stuck" after about 10 seconds. I carefully moved the variable redline indicator to see if it would start moving again. I want to add, that I put the word stuck in quotes, because I do not believe it to have actually physically been stuck, that is just the way it seemed when I watched it. I don't believe my moving it by hand helped at all, but all of a sudden, seemingly out of a nowhere, the redline quickly "slid" up about 2000 RPMs and then slowly started creeping up as the car warmed up. I went for a drive, and the redline eventually moved up to 8400 RPMs. I turned the car off, then back on, and it stayed at 8400 RPMs. So I took the cluster circuit board back out, put everything back together, and reinstalled it in the car, and took it for another drive. It still worked properly.

Hooray, I thought it was fixed. But the next morning after letting the car sit, I went for a drive, and it is still acting as it was before I took the cluster apart.

So let's recap, for the TL;DR crew.

1. Cluster has an issue with the variable redline.
2. Took the cluster out to try and fix it.
3. It all of a sudden started working after messing with it, but then stopped working the next day.

BMW says it's an issue with the cluster (which I could agree with) but they want $1000.00 to fix it. I am not paying that much for a new cluster, nor am I even paying the $700 it would cost for a used cluster to get coded to my car. Especially when it isn't even a guaranteed fix.

So I wanted to know from someone who might have some experience with our clusters, or how they work, what specifically might be causing my issue? Is it at all likely it's a faulty oil temp sensor, or is it most likely an issue with the cluster itself? If it's most definitely the cluster, what part, specifically would be at fault here? Is it likely it's the POT (or whatever it is) that controls the sliding redline indicator, or could it be the circuit board itself? My thought was to buy a damaged, broken, or otherwise not working M3 gauge cluster for cheap, take the POT out, and solder it into my cluster to avoid buying a more expensive, working cluster and having it coded. I just wasn't sure if this would work. Any ideas on if this is a decent approach, if it will likely fix my issue, or where I can get a broken cluster for cheap?

[Time Lord]

Sucks your not in the states to just swap with someone else to see if it fixes the issue

[BPMSport]

It's either the cluster or the dme software. I think you're going to run into a dead end if you try self repairing the cluster without knowing what's actually causing the issue. The redline is electronically controlled by the dme.

[Rat3d ///M]

Originally Posted by Time Lord

Sucks your not in the states to just swap with someone else to see if it fixes the issue

That's actually a good idea. Plenty of M3's in this area, just need to find someone willing to let me use their cluster for a minute.

Originally Posted by Mike Benvo

It's either the cluster or the dme software. I think you're going to run into a dead end if you try self repairing the cluster without knowing what's actually causing the issue. The redline is electronically controlled by the dme.

I remember the previous owner said he has had BMW try and reflash the DME module twice. Not sure if there is any truth to that, or if I am remembering incorrectly.

Are there any implications to borrowing a cluster from someone to see if theirs works in my car? I know there are issues with mileage and coding, is a simple plug n play swap without any adverse effects to try out a different cluster in my car for a minute, and swap back with no issues to either car or the clusters?

[Time Lord]

I don't think so, I would at least try it. Dme ' s are expensive I just had mine replaced under warrenty

[Jsantos]

I somehow stumbled on this thread searching online about this issue. I am having the same issue where the variable redline on my 08 E90 M3 would move randomly and be stuck there for days even when the car has properly warmed up.

I know this is an old thread but i recently purchased this car and this issue is making me cautious on when to know my car has fully warmed up.

OP did you ever get this issue fixed? Were you succesful with swapping out a cluster and see if it ever was a programming issue?

I'd really appreciate the input.

[Rat3d ///M]

Issue has been fixed for quite some time. Instead of buying a whole new cluster and deal with having it coded to my car, I found a member on here selling cluster parts. He was going to sell me a motor that controls the variable tach, but upon trying to unsolder my motor in my cluster to take it out to switch it with the one from the Cruise Control dial to see if the problem switched sides (confirming the motor itself was in fact bad) the redline indicator fixed itself. I assume that it was acting up due to a bad connection on the back at one of the solder points. It's been several months and I haven't had one issue since I resoldered the motor at the 4 connecting points.

My advice to you, is to take your cluster out, take it apart, and resolder the connections on the back of the circuit board where the motor that drives the variable redline indicator connects. If this does not fix the issue, maybe try to switch the motor with the cruise control motor like I was going to, to see if the issue switches sides. If it does, you know it is the motor that is bad, and you can pick up a motor from someone on here for cheap ($50?) solder it in and be on your way.

Hope that makes sense.

[Jsantos]

Sounds like better way to spend $1k for a cluster and coding it. Thanks for the advice. Looking in to it asap

[Jsantos]

Bumping up this post for other owners who experience this. I think i fixed the issue.

I did reset the ECU/DME and let it sit for a couple of mins. So far its been a couple of days and the Variable Redline started acting normal again.