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Discussion Starter · #1 · (Edited)
Hi everyone,

So to make a very long story short, or you can read here... my battery, which I thought the problem was fixed, is not the battery at all. After several weeks at the Mercedes dealership, they have determined that the 'module' that connects/disconnects my HV battery and my 12v battery is 'blown'. Thus draining my 12v battery very quickly and killed my new battery within a week or two.

I can't seem to get a straight answer on what the part is, but they are quoting me $4200 ($3500 for a refurbished) for the part and $2000 for labor.

They suggested that I could connect to a trickle charger every time I turn off my car. Given the location of the battery and the fact that I live in a townhouse without access to a power outlet, this doesn't seem to be a great solution.

Has anyone else had this issue? What is the part? Is there a reasonable workaround? Is a workaround even safe?

One of the mechanics said that this part disconnects in the event of an accident to keep the car from blowing up. They also mentioned that the damage could have happened from a minor hit to the car.

I would love any suggestions on fixes and to hear if you had this experience.

Thank you!

UPDATE: I finally was able to get the part that needs to be replaced. The M-B dealership said it was the power-electronics module. This is the $4k part.
 

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After several weeks at the Mercedes dealership, they have determined that the 'module' that connects/disconnects my HV battery and my 12v battery is 'blown'.

I can't seem to get a straight answer on what the part is, but they are quoting me $4200 ($3500 for a refurbished) for the part and $2000 for labor.

One of the mechanics said that this part disconnects in the event of an accident to keep the car from blowing up. They also mentioned that the damage could have happened from a minor hit to the car.
Well that’s some useless drivel from your M-B dealer! First and foremost, I don’t believe that the NHTSB has any report of a smart fortwo having “blown up.”

Have you been in a fender bender (minor hit)? It sounds like they are describing the “pyro fuse” which can blow when the accident sensors detect trouble and “disable” ED.

$4,200 repair makes no sense if the service is just to replace the pyro fuse???
 

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Discussion Starter · #3 ·
Well that’s some useless drivel from your M-B dealer! First and foremost, I don’t believe that the NHTSB has any report of a smart fortwo having “blown up.”

Have you been in a fender bender (minor hit)? It sounds like they are describing the “pyro fuse” which can blow when the accident sensors detect trouble and “disable” ED.

$4,200 repair makes no sense if the service is just to replace the pyro fuse???
No, I haven't been in a fender bender but I do park in an alley... it's not impossible that someone slightly tapped the car. It doesn't have any damage.

I don't know what part it is... they don't tell me. I have asked several times for the quote to be emailed to me and the exact name of the part but I can't seem to get a straight answer. They call it a 'module'. The module/part that connects the HV and 12v batteries and tells the 12v to disconnect when the car is off. The $4200 is the cost of the part only! This 'module'.
 

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Only thing I can think of connecting the two is the link for the DC-DC converter, or whatever terminology Daimler/Smart uses. Those are supposedly expensive.

EDIT-. What model year is this? Someone here had a different issue that caused his 12 V to boil basically. Smart/Mercedes took care of it under warranty albeit a while ago...

Sent from my moto g(7) power using Tapatalk
 

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The battery test unit uses the work "CONTACTOR." With the car not turned on, the 12v battery is not connected to the HV battery and the test unit says the the "CONTACTOR" is OFF. When the key is turned ON, then the test unit shows that the "CONTACTOR" is ON, meaning that it is connected to the 12v battery. Is that where the problem is? Your guess is as good as mine.

Len
 

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No, I haven't been in a fender bender but I do park in an alley... it's not impossible that someone slightly tapped the car. It doesn't have any damage.

I don't know what part it is... they don't tell me. I have asked several times for the quote to be emailed to me and the exact name of the part but I can't seem to get a straight answer. They call it a 'module'. The module/part that connects the HV and 12v batteries and tells the 12v to disconnect when the car is off. The $4200 is the cost of the part only! This 'module'.
What they are telling you does not make any sense. As an engineer, l hate in when someone thinks a concept is only understandable to a non-specialist if it is "dumbed down" until it is gibberish.

There is a DC-DC converter that converts the 370 volts in the HV battery to about 14 volts for charging the 12V battery and powering the lights, windows, wipers etc - i.e. it serves the same function as the alternator/generator in an IC engine car. Unfortunately this converter is integral with the Power Electronics Control Unit (N129/1) which is the power inverter (DC to 3 phase AC) and controller (the "throttle") for the motor. N129/1 is the biggest aluminum box you will see if you lift the carpet and open the engine compartment behind the seats. Like every other component on the Smart ED is it outrageously overpriced. I have no idea why it would cost $2000 labor to replace it because it is jsut a simple part replacement and some software resetting.

I can only assume that MB deliberately overprices parts and service on Smart ED' becasue MB management regards the smart as an "embarrassment" to their snobbish upscale MB Brand and want to speed the flow of the remaining ED's and EQ's into the junkyards.

Of course, you might be able to find a junkyard N129/1, install it yourself, then have the dealer do any software reconfiguring that is needed.
 

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In your other thread Len pointed out a potential software update. I’m guessing it hasn’t been done either due to the car not qualifying or just not done yet. You should have received a receipt with that detail in there if it had been updated. At this point try to figure out if it’s an open campaign and have it done (at rightful no cost to you)…
 

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If your car spent time at a dealership for any reason, they should have updated your software automatically if it needed it, but they should have also told you they did. With your VIN they should be able to tell you if your car has had that update or not.

Len,
 

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Idea...
If the defective ECU is discharging the 12V battery, you can wire a switch to the negative terminal of the battery and flip the switch to disconnect the 12V battery when the car is not in use. Or a more sophisticated method would be to wire the keyswitch (if it is a switch and not a Hall device) to a relay (solid-state relay would be ideal) on the 12V negative lead of the battery. Your clock/and radio setting would be lost - but at least the car is still usable.
 
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