Key battery low warning on both keys

kkasson · 12-08-2020, 08:14 PM

Wondering if anyone has seen this weird problem before. Both of my keys have started showing the low key battery warning (CC ID 65). Both of the remotes still work fine. I actually cut one open to replace the battery thinking it was just dying, but it measured 3.25 volts and appears to work fine. It was after that that I noticed the same thing happens with the second key...this all started within about a week so I don't think the keys are actually the problem.

Any ideas? I didn't find any relevant codes and I cleared everything just in case; I also disconnected the battery for an hour and it's still happening. I assume it's something with the key slot or the CAS module...I'm looking through the wiring diagrams to try to figure out where to start but I wanted to check if anyone else has had this problem before wasting time poking around.

gbalthrop · 12-08-2020, 09:20 PM

See Posts #3 & #4 in the following recent thread:
https://www.e90post.com/forums/showthread.php?t=1781127

George

kkasson · 12-08-2020, 09:37 PM

Thanks! Can't believe I missed that thread from only a couple days ago, I tried to search but only found the normal threads about dead batteries.

Checking the wiring near the CAS was going to be my first step anyway, looks like that will be the plan. The car battery itself is good, reads around 12.55 volts.

The starter died 3 or 4 months ago and I did remove the interior trim to do some tests (can't remember what I was looking for down there but I remember having it disassembled.) There could be a pinched wire or something, although everything was fine for the first few months after that. Maybe something is loose and the insulation finally wore through. That would make sense that the problem would show up now if in fact the key fob was actually draining due to never being charged over the last couple months, although again it did read 3.25 volts which doesn't seem like it should be low enough to trigger the warning. I'll check the wiring in any case.

(By the way, many thanks for all of the detailed posts, George. I've found other posts of yours lots of times while diagnosing things and they're always extremely helpful. Thank you!)

kkasson · 12-10-2020, 01:18 PM

No luck so far. I checked the footwell and didn't find any obvious signs of damage. I've attached pictures of the main harness and the CAS connectors. Everything looks fine to me.

I can't find anything on how the circuit actually works other than that the ribbon cable connects the key slot to the CAS. I'm not really sure where to go from here - I did find a thread somewhere else where someone actually did have two key batteries go bad at exactly the same time, so maybe that really is the problem and it's just a crazy coincidence. My second key did seem to work for a couple days before it also started giving the warning.

I'd already ordered the key battery before I opened the remote to check the voltage, so I'll just try installing the new battery when it gets here on Saturday and see if anything changes.

kkasson · 12-12-2020, 02:09 AM

So, believe it or not, it appears that after 14 years both batteries did just decide to die within the same week. I installed the new battery in the first fob and it's working fine again. Second fob still has the old battery and is showing the low battery warning. The new battery was only at 2.9 volts and the original is still around 3.2, so I guess it must somehow detect more than just the voltage to know if the charge is low.

Just a heads up for anyone who might stumble upon this thread, I did run into a few difficulties installing the new battery. The bottoms of the terminals on the new battery are slightly wider than the original and they don't fit in the PCB correctly. It seems like it's installed but the bottom of the terminals are too big and will hold the battery away from the surface of the board. I ended up cutting the larger terminal from both batteries and carefully soldering the end of the old terminal onto the new one. I was able to carefully trim away some of the smaller terminal to make it fit. You can probably shave away some of the bigger terminal as well, but I went too far and broke it so I salvaged the terminal from the old battery instead.

As far as I could tell nobody sells the actual same battery that BMW uses, it looks like all of them will have this problem. You might be able to trim some of the plastic from the back half of the key fob and leave the battery higher off the board instead.

12-08-2020, 08:14 PM	#1
kkasson Lieutenant 187 Rep 589 Posts Drives: 07 BMW 328i, 08 BMW 528i Join Date: Jun 2015 Location: CA iTrader: (0)	Key battery low warning on both keys Wondering if anyone has seen this weird problem before. Both of my keys have started showing the low key battery warning (CC ID 65). Both of the remotes still work fine. I actually cut one open to replace the battery thinking it was just dying, but it measured 3.25 volts and appears to work fine. It was after that that I noticed the same thing happens with the second key...this all started within about a week so I don't think the keys are actually the problem. Any ideas? I didn't find any relevant codes and I cleared everything just in case; I also disconnected the battery for an hour and it's still happening. I assume it's something with the key slot or the CAS module...I'm looking through the wiring diagrams to try to figure out where to start but I wanted to check if anyone else has had this problem before wasting time poking around.
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12-08-2020, 09:20 PM	#2
gbalthrop Brigadier General 2769 Rep 4,098 Posts Drives: 2007 328xi E91 Join Date: May 2017 Location: Fairfax Co, VA iTrader: (0)	See Posts #3 & #4 in the following recent thread: https://www.e90post.com/forums/showthread.php?t=1781127 George
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12-10-2020, 01:18 PM	#4
kkasson Lieutenant 187 Rep 589 Posts Drives: 07 BMW 328i, 08 BMW 528i Join Date: Jun 2015 Location: CA iTrader: (0)	No luck so far. I checked the footwell and didn't find any obvious signs of damage. I've attached pictures of the main harness and the CAS connectors. Everything looks fine to me. I can't find anything on how the circuit actually works other than that the ribbon cable connects the key slot to the CAS. I'm not really sure where to go from here - I did find a thread somewhere else where someone actually did have two key batteries go bad at exactly the same time, so maybe that really is the problem and it's just a crazy coincidence. My second key did seem to work for a couple days before it also started giving the warning. I'd already ordered the key battery before I opened the remote to check the voltage, so I'll just try installing the new battery when it gets here on Saturday and see if anything changes. Attached Images
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12-12-2020, 02:09 AM	#5
kkasson Lieutenant 187 Rep 589 Posts Drives: 07 BMW 328i, 08 BMW 528i Join Date: Jun 2015 Location: CA iTrader: (0)	So, believe it or not, it appears that after 14 years both batteries did just decide to die within the same week. I installed the new battery in the first fob and it's working fine again. Second fob still has the old battery and is showing the low battery warning. The new battery was only at 2.9 volts and the original is still around 3.2, so I guess it must somehow detect more than just the voltage to know if the charge is low. Just a heads up for anyone who might stumble upon this thread, I did run into a few difficulties installing the new battery. The bottoms of the terminals on the new battery are slightly wider than the original and they don't fit in the PCB correctly. It seems like it's installed but the bottom of the terminals are too big and will hold the battery away from the surface of the board. I ended up cutting the larger terminal from both batteries and carefully soldering the end of the old terminal onto the new one. I was able to carefully trim away some of the smaller terminal to make it fit. You can probably shave away some of the bigger terminal as well, but I went too far and broke it so I salvaged the terminal from the old battery instead. As far as I could tell nobody sells the actual same battery that BMW uses, it looks like all of them will have this problem. You might be able to trim some of the plastic from the back half of the key fob and leave the battery higher off the board instead.
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12-08-2020, 09:37 PM	#3
kkasson Lieutenant 187 Rep 589 Posts Drives: 07 BMW 328i, 08 BMW 528i Join Date: Jun 2015 Location: CA iTrader: (0)	Thanks! Can't believe I missed that thread from only a couple days ago, I tried to search but only found the normal threads about dead batteries. Checking the wiring near the CAS was going to be my first step anyway, looks like that will be the plan. The car battery itself is good, reads around 12.55 volts. The starter died 3 or 4 months ago and I did remove the interior trim to do some tests (can't remember what I was looking for down there but I remember having it disassembled.) There could be a pinched wire or something, although everything was fine for the first few months after that. Maybe something is loose and the insulation finally wore through. That would make sense that the problem would show up now if in fact the key fob was actually draining due to never being charged over the last couple months, although again it did read 3.25 volts which doesn't seem like it should be low enough to trigger the warning. I'll check the wiring in any case. (By the way, many thanks for all of the detailed posts, George. I've found other posts of yours lots of times while diagnosing things and they're always extremely helpful. Thank you!)
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