Battery/alt stop vehicle. Burning smell. What do I do? 2003 e320
Out Of Control!!
Joined: Apr 2019
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From: Silicon Valley
W212 MY'14 M276-3.5NA @75kMi
drain from 12.5 to 10V
here is a video I took when it was happening: https://ufile.io/2fwmzk30
In this video the battery was at 12.5 before I started car then it dropped to like 11.9 when car started then it went back up to 12.01 before the fluctuation began, one point in the video it dropped all the way down to 10 volts so something is really draining it heavy. the burning smell im 95% sure it was coming from the front of the car so no I didn’t open up the bcm, when i thought the bcm was my issue I just bought a whole new one because someone told me the bcm is hard to repair if you aren’t experienced
In this video the battery was at 12.5 before I started car then it dropped to like 11.9 when car started then it went back up to 12.01 before the fluctuation began, one point in the video it dropped all the way down to 10 volts so something is really draining it heavy. the burning smell im 95% sure it was coming from the front of the car so no I didn’t open up the bcm, when i thought the bcm was my issue I just bought a whole new one because someone told me the bcm is hard to repair if you aren’t experienced
Can you unplug the control connector from your new alternator? (output should then go to betwen 13 and 14V to a good stable default voltage value)
I think the burning smell up front is the alternator acting as a drain when the ECU/F-SAM give it crazy control values. Then ALT output swings to deliver the value requested... I've seen that first hand.
The BCM when toasted by a high-voltage switching spike can not be repaired. Everything inside is shot all the way to a hole in CPU microcontroller.... only 1% chance to be lucky with a minimal spike.
FYI: switching Low batteries is what kills the BCM.
Keep charging/floating your battery to make up for the discharge drain you car is causing.
The charging system in these cars can get pretty downright disfunctional. Keep an eye on it 👀
Last edited by CaliBenzDriver; Jan 25, 2022 at 09:02 PM.
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2003 e320
Originally Posted by Heguli;[url=tel:8499753
8499753]So your battery voltage is around 12 volts when the engine is running? Then you have a bad alternator. I've had cars with alternators that have drained the battery, and they had burning smell.
edit/ Just read previous posts, and you should have a good alternator.
edit/ Just read previous posts, and you should have a good alternator.
yes I have a new Remy alternator so I’m not sure what my issue is. So many electrical problems with this car. I have no shops near me because I’m from the middle of nowhere, I would have been brought it by a shop if I could. I’ve been using a voltmeter to test fuses and pull them if they were draining, I only found 2 that were doing this, one in the driver Sam compartment and audio gateway fuse from rear Sam . Once I pulled them out my car stopped draining while it is off and now only drains when I turn the car on. Maybe I missed some other fuses. Lmao this is a nightmare.
Last edited by azer carrot; Jan 25, 2022 at 08:11 PM.
Out Of Control!!
Joined: Apr 2019
Posts: 11,922
Likes: 6,775
From: Silicon Valley
W212 MY'14 M276-3.5NA @75kMi
yes I have a new Bosch alternator so I’m not sure what my issue is. So many electrical problems with this car. I have no shops near me because I’m from the middle of nowhere, I would have been brought it by a shop if I could. I’ve been using a voltmeter to test fuses and pull them if they were draining, I only found 2 that were doing this, one in the driver Sam compartment and audio gateway fuse from rear Sam . Once I pulled them out my car stopped draining while it is off and now only drains when I turn the car on. Maybe I missed some other fuses. Lmao this is a nightmare.
SAM as Pwr Controllers:
The car power is controlled by SAM computers. They decide what module gets powered ON or OFF.
When SAM are glitched by low voltage conditions, they do crazy stuff and may not switch off controllers put the car to sleep or talk right with ALT.
Catch-22:
When COMAND module is crazy it doesn't talk to SAM to switch off audio interface that appears to be causing drain...
Many of these cars have a form of drain: small, medium or large. To regain battery peace, keep the battery floated to make up for small/medium drains.
Last edited by CaliBenzDriver; Jan 25, 2022 at 06:29 PM.
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2003 e320
Originally Posted by CaliBenzDriver;[url=tel:8499763
8499763[/url]](I can not see your MOV file)
Can you unplug the control connector from your new alternator? (output should then go to betwen 13 and 14V to a good stable default voltage value)
its Dark now but I will do in the morning. I haven’t even heard of doing this before hopefully it will help.
I think the burning smell up front is the alternator acting as a drain when the ECU/F-SAM give it crazy control values. Then ALT output swings to deliver the value requested... I've seen that girst hand.
Good Information thank you. I haven’t really checked the front Sam fuses or relays to much. Could it be a relay issue? I don’t know how to check them. the last time I smelled it burning was before I changed the alternator about 6 months ago
The BCM when toasted by a high-voltage switching spike can not be repaired. Everything inside is shot all the way to a hole in CPU microcontroller.... only 1% chance to be lucky with a minimal spike.
FYI: switching Low batteries is what kills the BCM.
so the bcm can get easily fried just if I switch them out? I removed battery when I switched them. Maybe I’m not understanding what u mean? But yes I have had to jump the car multiple times in the past and had to run on the cars recharge system or else I would have been stranded, and had to drive with all the malfunctions so I probably only made it worse. I have 2 battery’s (bought new battery aswell, thinking that was issue) I tend to switch them out and charge one on trickle charger overnight.
Keep charging/floating your battery to make up for the discharge drain you car is causing.
The charging system in these cars can get pretty downright disfunctional. Keep an eye on it 👀
Can you unplug the control connector from your new alternator? (output should then go to betwen 13 and 14V to a good stable default voltage value)
its Dark now but I will do in the morning. I haven’t even heard of doing this before hopefully it will help.
I think the burning smell up front is the alternator acting as a drain when the ECU/F-SAM give it crazy control values. Then ALT output swings to deliver the value requested... I've seen that girst hand.
Good Information thank you. I haven’t really checked the front Sam fuses or relays to much. Could it be a relay issue? I don’t know how to check them. the last time I smelled it burning was before I changed the alternator about 6 months ago
The BCM when toasted by a high-voltage switching spike can not be repaired. Everything inside is shot all the way to a hole in CPU microcontroller.... only 1% chance to be lucky with a minimal spike.
FYI: switching Low batteries is what kills the BCM.
so the bcm can get easily fried just if I switch them out? I removed battery when I switched them. Maybe I’m not understanding what u mean? But yes I have had to jump the car multiple times in the past and had to run on the cars recharge system or else I would have been stranded, and had to drive with all the malfunctions so I probably only made it worse. I have 2 battery’s (bought new battery aswell, thinking that was issue) I tend to switch them out and charge one on trickle charger overnight.
Keep charging/floating your battery to make up for the discharge drain you car is causing.
The charging system in these cars can get pretty downright disfunctional. Keep an eye on it 👀
Thread Starter
Junior Member
Joined: Aug 2020
Posts: 29
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2003 e320
Out Of Control!!
Joined: Apr 2019
Posts: 11,922
Likes: 6,775
From: Silicon Valley
W212 MY'14 M276-3.5NA @75kMi
I am not familiar with all the specifics of your W211 chassis... yet I can recommend you check:
> F-SAM for water intrusion, bad GND's.
> R-SAM for solderless control board pins, bad GND's.
> BCM: these modules are fragile and can not be repaired!
I don't know ALL your BCM circuit functions (besides switch AUX to help MAIN Batt. etc)
It's almost as if you could be better off unplugging BCM to prevent additional smokey problem for now. To preserve it, you don't want the BCM to switch any heavy power load or activate any battery K-Relays coils.
I have not tested how viable your car may be with a disconnected BCM and K-relays resting... I think they will stay in default position.
When you car is running below 12.5V down to 10v is when Sam's drive themselves nuts. Imagine how low is a 400Amps starter crank from an undercharged battery? Simply do a car reboot to reset SAM's.
✌️
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2003 E320 Mercedes
2003 E320 dead battery overnight
yea you’re right. I’m not 100% sure if that’s the only thing that’s wrong though. Ive had battery charging issues since I’ve gotten this car. a messed up alt wouldn’t cause the battery to die from sitting overnight would it? Sorry for the stupid questions im 17 bought this as my first car and I really regret it tbh, to many electrical issues. Nice car but to much maintenance
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Joined: Apr 2007
Posts: 633
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From: USA
2006 E320 CDI
I’ve been having issues with my car being dead after being left overnight, getting electrical consumers switched off sign a lot. replaced battery in my trunk and worked good for about a month, then decided to start dying again within this past week. Just trickle charged my battery overnight last night and I went to put it back in the trunk about 20 mins ago, at first I got electrical consumers switched off(even after charging all night) then I got the batter/alt light and no brakes light. Started smelling some burnt plastic, Did some research here and turns out burning smell is from alternator so now I’m wondering if I have to get a whole new alt or if I can just do the voltage regulator replacement? How can I test to figure out if I can just replace VR and not whole alternator? Was thinking I just had a parasitic drain draining my battery but now it’s starting to seem like it’s something else. Or maybe I have a drain and alt is bad?? Idk Already replaced my Sam and didn’t help. Really don’t have a lot of money to spend so need to know if I can do the vr diy or if I just need to go ahead and get alt. Tested my battery’s and they both are strong. Would appreciate the help a lot!
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