Battery Problem

Walkurie · 02-20-2012, 09:08 AM

I replaced my first battery at 29,000 miles and it seems as though the second will have an equally short life. It has completely discharged twice in the past year. The car has 47,400 miles on it now. I'm out of warranty.

From all indications and after researching the archives, it seems as though it is a defective TCU. The short term memory for the odometer, clock, average speed, mileage, etc. wipes out after every driving session. I drive the car daily, have a 12 mile commute. Should be ideal for proper cycling of the battery. I do supplement the charging on a weekly basis.

So my questions are...

Is a TCU replacement possible by a DIY'er? I looked in the TIS and it refers to a programming process. Doubt I can take this on without advice.

How much does a new TCU cost? When done by a dealer? Can an indy do it?

Other postings have indicated that at least one dealer opened up a PUMA with the factory on this problem. Has anyone heard of any updates on this?

Any advice is appreciated.

WestCDA · 02-20-2012, 11:24 AM

That's a pretty expensive solution, based on an assumption of a defective TCU. The symptoms you describe (battery fully discharging, need to keep 'supplementary' charged, losing memory settings) sound more to me like a charging system problem - I'd get that checked, as well as check for parasitic loads on the battery when the car is shut off.

gferil · 02-20-2012, 12:55 PM

The defective TCU is only one possible problem. Like WestCDA said above, you might want to check to see if your charging system is working properly.

Also, get yourself a multimeter and check the current being drawn when your car is in the "off" position, if it's more than 70mA then you probably have something drawing excess current, and the TCU is one culprit.

Replacing the TCU is fairly simple, remove the trunk carpeting to access the TCU, remove four bolts that hold it in place, unplug three antenna cables and main wire harness, and then installation is reverse of removal. The hardest part for you will probably be removing the trunk carpet.

But I'd check your charging system and current draw before you assume it's the TCU. Also, is your bluetooth system working correctly? Cause if so, you can rule out the bad TCU.

Pheonix · 02-20-2012, 01:39 PM

My battery was replaced at around 18k miles. Then i started to have problems with the battery went death after couple days. It turned out to be a defective TCU. Every 30 minutes, i would "waken up" and searches for Bluetooth device (15 minutes at a time). Apparently, it was draining 3A and the battery will be drained in no time. The TCU was replaced under warranty.
I don't have any advice for you but i don't think it is worth replacing it (if it is the culprit). I don't even use mine and not sure if there is anyway to disable it completely.
Anyhow, as those other members mentioned. You could start by checking to see how much current is being drained. Also, get a battery tender and hook it up right away because your batttery will get degraded everytime it drained. Good luck

02-20-2012, 09:08 AM	#1
Walkurie Lieutenant 9 Rep 452 Posts Drives: 06 M Roadster / 99 Jaguar XK8 Join Date: Mar 2010 Location: Surf City, CA iTrader: (2)	Battery Problem I replaced my first battery at 29,000 miles and it seems as though the second will have an equally short life. It has completely discharged twice in the past year. The car has 47,400 miles on it now. I'm out of warranty. From all indications and after researching the archives, it seems as though it is a defective TCU. The short term memory for the odometer, clock, average speed, mileage, etc. wipes out after every driving session. I drive the car daily, have a 12 mile commute. Should be ideal for proper cycling of the battery. I do supplement the charging on a weekly basis. So my questions are... Is a TCU replacement possible by a DIY'er? I looked in the TIS and it refers to a programming process. Doubt I can take this on without advice. How much does a new TCU cost? When done by a dealer? Can an indy do it? Other postings have indicated that at least one dealer opened up a PUMA with the factory on this problem. Has anyone heard of any updates on this? Any advice is appreciated. __________________ Vibra Technics engine mounts / Rogue trans mounts / Stoptech brakes / original owner
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02-20-2012, 11:24 AM	#2
WestCDA Second Lieutenant 7 Rep 273 Posts Drives: 2006 Z4R 3.0si Join Date: May 2011 Location: Calgary, Alberta iTrader: (0)	That's a pretty expensive solution, based on an assumption of a defective TCU. The symptoms you describe (battery fully discharging, need to keep 'supplementary' charged, losing memory settings) sound more to me like a charging system problem - I'd get that checked, as well as check for parasitic loads on the battery when the car is shut off.
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02-20-2012, 12:55 PM	#3
gferil Captain 30 Rep 740 Posts Drives: 06 Z4MC Join Date: Dec 2010 Location: San Francisco, CA iTrader: (6)	The defective TCU is only one possible problem. Like WestCDA said above, you might want to check to see if your charging system is working properly. Also, get yourself a multimeter and check the current being drawn when your car is in the "off" position, if it's more than 70mA then you probably have something drawing excess current, and the TCU is one culprit. Replacing the TCU is fairly simple, remove the trunk carpeting to access the TCU, remove four bolts that hold it in place, unplug three antenna cables and main wire harness, and then installation is reverse of removal. The hardest part for you will probably be removing the trunk carpet. But I'd check your charging system and current draw before you assume it's the TCU. Also, is your bluetooth system working correctly? Cause if so, you can rule out the bad TCU.
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02-20-2012, 01:39 PM	#4
Pheonix Major 379 Rep 1,002 Posts Drives: 2007 Z4 M Coupe 2012 e93 M3 Join Date: Sep 2008 Location: Bay Area, CA iTrader: (8) Garage List 2007 BMW/Z4MC [0.00]	My battery was replaced at around 18k miles. Then i started to have problems with the battery went death after couple days. It turned out to be a defective TCU. Every 30 minutes, i would "waken up" and searches for Bluetooth device (15 minutes at a time). Apparently, it was draining 3A and the battery will be drained in no time. The TCU was replaced under warranty. I don't have any advice for you but i don't think it is worth replacing it (if it is the culprit). I don't even use mine and not sure if there is anyway to disable it completely. Anyhow, as those other members mentioned. You could start by checking to see how much current is being drained. Also, get a battery tender and hook it up right away because your batttery will get degraded everytime it drained. Good luck
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