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E91 M3 here. At night, when headlights are on, only

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E91 M3 here. At...

E91 M3 here. At night, when headlights are on, only speedometer and tachometer back-light dims. The idrive, a/c display and cluster display remain in the day mode. The problem seems to be intermittent, so every time I took the car to a dealer I could not demonstrate the problem.

Mechanic's Assistant: Have you checked the fuses? Have you checked the bulbs?

Haven't checked the fuses; as for the bulbs, how can they be at fault? The displays all work; they do not dim at night i.e. much too bright.

Mechanic's Assistant: What year is your M3?

2013

Mechanic's Assistant: Are you fixing your M3 yourself? What have you tried so far?

Nothing, except extensive googling. This is a new problem. Seemed to come up after an airbag was replaced by the dealer under the Takata recall. No clue how it could be relevant, but still...

Mechanic's Assistant: Anything else you want the mechanic to know before I connect you?

I cannot think of anything. Really weird problem.

Submitted: 1 month ago.Category: BMW
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Answered in 6 hours by:
3/16/2018
BMW Mechanic: Danny, ASE Certified Technician replied 1 month ago
Danny
Danny, ASE Certified Technician
Category: BMW
Satisfied Customers: 4,282
Experience: ASE Master Technician with L1 advanced engine performance, VW Certified, former US Army mechanic
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Wait so are you saying that some of the instrument cluster lights dim but not the rest of them? So like the fuel gauge and coolant temp stay bright but not the speedo or tach? Are your headlights in automatic mode with the headlight switch? Does it do it in both Auto and manual headlight on mode? Go into the settings on the iDrive and look for display settings and see what that is set at and try altering it.
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Customer reply replied 1 month ago
I am saying exactly that. Speedometer tachometer and all the other dial gauges and panel lights (like radio buttons) dim normally. However 3 displays are exception to that: AC display (just the display, buttons dim normally), the LCD display on the gauge panel and the iDrive display do not dim. On top of that, the problem seems to be intermittent. I am still experimenting to figure out what event triggers this problem.The problem happens both in manual and auto headlight modes. It seems like if it appers, it appears in all modes. If it was not triggered, all modes work correctly.I have played with iDrive. Brightness settings do not solve the problem. It adjust it as it would normally, but this has nothing to do with dimming, it is just daytime brightness. Moreover, it adjusts just the iDrive display, those brightness settings have no effect on the 2 red LCD displays.
Customer reply replied 1 month ago
Also, there are no fault codes. The only fault code that was there is for list power (probably due to the airbag replacement). I have cleared it, and it had no effect on the dimming problem.
Customer reply replied 1 month ago
Lost power*
BMW Mechanic: Danny, ASE Certified Technician replied 1 month ago
Ok what is the fault code number that you have? That's important info you should have told me before because a faulty or noncommunicative control module can cause this problem.The AC head unit and iDrive are control module and, and the way they know that the lights are on is by the comfort module sending the info over the can bus network. When there's a faulty control module, depending on which one it is, it may be the one responsible for sending or relaying that info over the can bus network, or it might be sending electronic noise over the can bus network that is jamming communication.That seems to be the problem here.So, I need the fault code number itself not the fault code description.
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Customer reply replied 1 month ago
This is not something I knew before a couple hours ago. I took it to a mechanic I know, so we briefly looked at the codes and reset them, however we did not take note of the code number. I'd have to wait for that fault come to return (if it returns at all). I'll let you know once I know the code or the fact that it is not coming back.
BMW Mechanic: Danny, ASE Certified Technician replied 1 month ago
Okay sounds good, you really need to probably take it to a BMW specialist unless you wanted to buy the Bavarian Technic scan tool which I believe is like $800. You need to scan tool that can talk to the climate control module and the iDrive and scan them for faults.You mentioned that the airbags were replaced you don't have an airbag light on to you? What about an ABS light? Are there any warning lights anywhere on or any other system that doesn't function properly?
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Customer reply replied 1 month ago
Today we scanned it with some tool that was common with BMW and Porsche (that mechanic works mostly on Porsches). Looked like a big blue 5cm thick ipad with handles. Are you saying that a regular OBD2 reader won't pick this up?Yes, driver's airbag was replaced at the local BMW dealer as part of that huge Takata recall, not because it threw an error. No lights or warnings whatsoever. Other than the dimming issue, the car seems to be working 100% correctly.But even that seems to come and go as lighting conditions change (or as auto on/off function cycles through, still figuring that one out). Possibly when I open the car door. Typically, in the morning when I start the car it works correctly. Then I get out of the garage, leave the car to close the gate, and by the time I am back the problem is there. I always fail to notice the exact moment it fails.It behaves as if there is a separate light sensor for the dimming of the monitors and it is glitching. The problem seems to go away temporarily after the car is parked for more than an hour. Leaving the car alone (and locked) for like 5-10 min does not reset the problem. And very occasionally (have observed it only once) it self-corrects it while the car is running.Actually... now that I think about it, it always works correctly in garage, but 50% of the time when outside... Weird. Maybe there is something about lighting conditions in the garage? Or maybe EM interference? Garage could be sort of Faraday cage... I am grasping straws here.Could a software update during airbag replacement have done it?
BMW Mechanic: Danny, ASE Certified Technician replied 1 month ago
Probably not on the software update that scan tools called an Autologic and I have the same one.He should be able to go in to the iDrive and climate control and look through it, but he would have to manually do that did you tell him about the problem or he just scan for engine fault codes?
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Customer reply replied 1 month ago
He just did a general scan. He told me ho scanned everything, but he definitely did not go into iDdrive or climate control specifically. I can ask him to do so on Monday, they are closed today.
Customer reply replied 1 month ago
it was an Autologic.
Customer reply replied 1 month ago
But he did go into some sort of event logger, because I have seen like 50 messages in a row (column, strictly speaking) that said that DSC was disabled (I have a habit of driving with DSC off). We did not find anything remotely related to the problem in there.
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