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      08-19-2019, 09:33 PM   #1
slidewayscoupe
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Hey all,

I just wanted to share for the archives my experience troubleshooting a failure of the comfort access feature that was seemingly unrelated to anything else.

Car:
2011.5 E90 M3 Sedan
53,000 miles

Symptoms:
I had just had the dealership replace my failing combox which was throwing an SOS light on the dash. After getting the car back from that procedure, it sat for a couple weeks. The next time I came out to drive, I couldn't unlock the car! None of the comfort access features worked, whether at the door handle or on the key fob. Once I used the metal key to unlock the door and climb inside, the keyless ignition feature was also malfunctioning. The dash just displayed the symbol of a key with a slash through it, as though it didn't recognize a key within the particular proximity that it requires. The key did work in the ignition once it was inserted and the car would start and run at that point.

I was convinced it was related to the combox swap so I came back to the dealership and convinced them that the keys likely needed reprogramming, blah blah blah. After a couple hours troubleshooting at the dealership, they told me that the car isn't seeing the keys and that the car also couldn't communicate with it's own antenna. They told me the next step was to replace the "diversity antenna amplifier" and see if that fixes it. At a quote of $550 for parts and labor just to throw parts at an unknown problem, I quickly declined and was on my way home. I spent the next several days researching "diversity antenna failures" and what that entailed. A lot of posts suggested that the failure of this antenna was also related to very poor AM/FM radio reception, however I live in a pretty populated area so it was difficult to tell if reception had fallen at all.

Long story short, along with all the above symptoms I was also able to find a very small place where the fob would work to lock and unlock the car which was directly above and below the shark fin antenna on the roof - I'm talking within about 4 inches on top or bottom, VERY CLOSE!

I pulled the trigger on a spare used part on eBay to replace my diversity antenna amplifier for about $40. ECS sells them new for around $350. Three plugs and two torx screws later and the replacement part worked to my surprise! So I hope this little write up can help folks in the future as I did gather from my research that this failure isn't entirely uncommon.
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      08-19-2019, 10:06 PM   #2
GeorgeA
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This is great news! Good work!
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      08-19-2019, 10:11 PM   #3
bvrider1
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Thanks for sharing OP!
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      08-25-2019, 07:28 AM   #4
su_root
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excellent.

could you add steps/instructions on how you replaced the diversity antenna amp? part numbers?
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      08-25-2019, 04:31 PM   #5
slidewayscoupe
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Quote:
Originally Posted by su_root View Post
excellent.

could you add steps/instructions on how you replaced the diversity antenna amp? part numbers?
Part numbers are right there in the photo but I'll specify:

https://www.ecstuning.com/b-genuine-...y/65209334692/

BMW Mfg part number 65209334692

It's incredibly simple, just have to pull the interior plastic trim piece off of the area of the upper brake light, GENTLY! I found that pulling down on the back portion, and then backwards on the front portion worked best. After that it's just two torx screws and three plugs - it's a simple swap.
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      08-30-2019, 02:16 PM   #6
Zechariaha
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Great job! Thanks for the info!
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