PLEASE HELP! TCU or bad battery?

Sam Vejvoda · 10-13-2022, 11:58 AM

My car has been experiencing battery drain and and will die in about a couple days. My speakers are popping even with car turned off.. my tail lights will randomly turn on also. I also have an SOS warning light on. I am not sure if this is my battery or TCU. I really need my car up and running and don't want to take it into the dealer! I tried to bypass the data lite radio with fiber optic but it didn't work. There is also a cord that is under the steering wheel that is supposed to be flashing red to tell you if the TCU is in good condition.. and it is not red. Please help! Any ideas?

TopJimmy · 10-13-2022, 01:30 PM

Unplug any accessories or hard-wired radar detectors. Get the fuse map from under the lid in the trunk. Check EACH of the fuse boxes for blown fuses, the car has a few fuse panels. Also check that the right Amperage fuse is in the correct slots, and no one mixed them up. If the problem is still there maybe remove the fuse for the entertainment system (to shut down the radio circuit) and see if the speaker pops stop.

When you said TCU (trans control unit?) did you mean the DME (main computer)?

There are other spots that have "electronic modules" like the FEM, which have non-replaceable fuses inside. Those are harder to diagnose.

Sam Vejvoda · 10-13-2022, 01:44 PM

Quote:

Originally Posted by TopJimmy

Unplug any accessories or hard-wired radar detectors. Get the fuse map from under the lid in the trunk. Check EACH of the fuse boxes for blown fuses, the car has a few fuse panels. Also check that the right Amperage fuse is in the correct slots, and no one mixed them up. If the problem is still there maybe remove the fuse for the entertainment system (to shut down the radio circuit) and see if the speaker pops stop.

When you said TCU (trans control unit?) did you mean the DME (main computer)?

There are other spots that have "electronic modules" like the FEM, which have non-replaceable fuses inside. Those are harder to diagnose.

I was referring to the telematics control unit. I heard when those go bad they can drain the battery and cause the SOS light to come on. I will also try and jump my car but it won't jump. The battery will be completely dead but I'll leave it hooked up for like 15 minutes and the car still won't even start. I brought the battery in to Auto Zone and they said it was a good battery… but I still have my doubts.

Jwild90 · 10-14-2022, 06:51 PM

Do a parasitic draw test. Very easy to do, just takes time to pull one fuse at a time and reading the amperage on voltmeter.

Obviously start from common items that typically cause battery drain issue like comfort access, tcu since u do have sos fault etc.

Sam Vejvoda · 10-15-2022, 01:53 PM

Quote:

Originally Posted by Jwild90

Do a parasitic draw test. Very easy to do, just takes time to pull one fuse at a time and reading the amperage on voltmeter.

Obviously start from common items that typically cause battery drain issue like comfort access, tcu since u do have sos fault etc.

How do I turn comfort access off? I do not have a screen

AlmondJayRoM3 · 10-28-2022, 09:51 AM

Have your battery tested. Can’t do any worthwhile electronics troubleshooting with a bad battery.

10-13-2022, 11:58 AM	#1
Sam Vejvoda Banned 3 Rep 56 Posts Drives: Bmw 228i Join Date: Oct 2022 Location: Florida iTrader: (0)	PLEASE HELP! TCU or bad battery? My car has been experiencing battery drain and and will die in about a couple days. My speakers are popping even with car turned off.. my tail lights will randomly turn on also. I also have an SOS warning light on. I am not sure if this is my battery or TCU. I really need my car up and running and don't want to take it into the dealer! I tried to bypass the data lite radio with fiber optic but it didn't work. There is also a cord that is under the steering wheel that is supposed to be flashing red to tell you if the TCU is in good condition.. and it is not red. Please help! Any ideas?
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10-13-2022, 01:30 PM	#2
TopJimmy Major General 5460 Rep 5,153 Posts Drives: 2023 M3 Comp xDrive Join Date: Jul 2019 Location: Chester County, PA iTrader: (5)	Unplug any accessories or hard-wired radar detectors. Get the fuse map from under the lid in the trunk. Check EACH of the fuse boxes for blown fuses, the car has a few fuse panels. Also check that the right Amperage fuse is in the correct slots, and no one mixed them up. If the problem is still there maybe remove the fuse for the entertainment system (to shut down the radio circuit) and see if the speaker pops stop. When you said TCU (trans control unit?) did you mean the DME (main computer)? There are other spots that have "electronic modules" like the FEM, which have non-replaceable fuses inside. Those are harder to diagnose. __________________ '18 F80 Base 6MT \| '19 F82 Exec DCT \| '18 F82 Comp Exec DCT \| '23 G80cx
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10-14-2022, 06:51 PM	#4
Jwild90 Private First Class 135 Rep 109 Posts Drives: 04'E46ZHP 20' F82M4Comp Join Date: Dec 2019 Location: NC iTrader: (0)	Do a parasitic draw test. Very easy to do, just takes time to pull one fuse at a time and reading the amperage on voltmeter. Obviously start from common items that typically cause battery drain issue like comfort access, tcu since u do have sos fault etc.
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10-28-2022, 09:51 AM	#6
AlmondJayRoM3 Captain 472 Rep 625 Posts Drives: 2016 M3 Join Date: Oct 2017 Location: Pittsburgh, PA iTrader: (0)	Have your battery tested. Can’t do any worthwhile electronics troubleshooting with a bad battery.
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