No really. A young guy at work came to me and ask if I worked on cars. Was ASE certified for about 25 years, but for the last 15 I have worked on forklifts. So I haven't kept up with a lot of stuff. Keep my fleet running and work on racecars. Anyway he and his brother tried to jump start another car with his 2014 Mercedes SLK and hooked the cables backwards. Fireworks, smoke and the SLK will not come back to life. He says he has checked all the fuses and they all check good. He's watched some youtube videos and still cannot get it running. I'm thinking the ECM has given its life to protect the fuses. Have not looked at it myself yet and was wondering if my OB2 scanner will connect to this car or do they have their own super cool diagnostic tools. Just kind of hoping to learn something and maybe save the kid some money before sending to the dealership.
Thank you.
Mndsm
MegaDork
1/31/24 11:05 a.m.
I'd bet a schnitzel he let the magic smoke out of something expensive.
I assume they tried another battery? By not come to life is there nothing like no lights dead or it won't try to crank or it won't catch and start?
In reply to Stampie :
Yes, he said they tried another battery. No lights, won't crank, nothing.
In reply to Mndsm :
That's what I'm thinking. You signature kinda sums it up.
there's probably a main fuse where B+ enters the underhood fuse block. Maybe not obvious to see and maybe not easy to swap. many years ago, i crossed cables when jumping a dead car off my 96 Probe GT and blew this main fuse. car was 100% electrically dead. changing the main fuse brought it back.
In reply to Mndsm :
It's called the stupid tax.
Everybody pays it at some point.
Life is hard. It's harder when you're stupid.
Mndsm
MegaDork
1/31/24 11:53 a.m.
In reply to earlybroncoguy1 :
If you're gonna be dumb you gonna be tough. Beer muscles help.
In reply to AngryCorvair (Forum Supporter) :
Will check that.
drock25too said:
In reply to Stampie :
Yes, he said they tried another battery. No lights, won't crank, nothing.
This again suggests that he got lucky and blew a main fuse he doesn't know about, if the ECU was fried the car would still show some signs of life, it just wouldn't fire up or possibly wouldn't crank. Some wiring harnesses have a connection with thin wire that acts as a large fuse, but you usually see that on really cheap basic cars (Samurai alternator wire for example).
drock25too said:
In reply to AngryCorvair (Forum Supporter) :
Will check that.
scroll down to "Engine Pre-Fuse Box", some pretty high-amperage stuff in there. I don't see one labeled "Main" but I'm betting there's one fuse to rule them all, where the B+ cable enters that box.
They usually have a protection relay that takes the heat. I don't know that car specifically but the 211 had one.
I got a fiver they dicked up the high speed can network lol. After going after the main block as the Angrycorvair wisely suggested if they are fine take your meter across pins 6&14 on the dlc and check for resistance, I'm guessing it's infinite. After that check power at dlc.
We had a benz come from the auction with a deab battery the truck driver jumped backwards. I got 26 hours off of that one to diag it and make three overlays to get it talking again.
Probably fried something expensively.
1980: My ex-wife asked a campus cop at college to jump start her car, a '73 Chevy Nova. He hooked them up backwards, X hit the starter, and the battery exploded. Battery acid and plastic battery casing bits everywhere. I was fortunate he wasn't standing there looking down at the battery when it exploded because we would have been sued by the Cop.
"I'm not responsible" (no E36 M3) he said and drove away. (Raises to question of how an irresponsible person can be a cop but I digress)
Another one. I had a 1980 Rabbit when in the early '80's. I jumped started someone while the engine was running and it fried the alternator. My family had a tire shop/mechanic shop and I had jumped dozens of vehicles with the engine running in the donor vehicles. Turned out VW's electronics could not handle this, which I would have known if I read the owner's manual carefully. The alternator was $250 in 1981 money ($839.01 in today's money) . I was making maybe $5.00/hour so $250 was over a week's pay.
The battery cable that burns up is called a fusible link if you're ever looking for the right word. I don't know that the SLK has one, but I'd start by putting a meter on the main battery connection at the fuse box.
AngryCorvair (Forum Supporter) said:
Any resolution on this?
Saw this back at the to and was wondering as well.
My vote is on fusible link as well. Probably a relatively cheap part as well.
In reply to grover :
Nothing is cheap on that car. Probably the Pre-Fuse box under the hood by the battery.
When AAA tries to jump a Benz, they get the terminals backwards. Feels like EVERY SINGLE TIME.
drock25too said:
No really. A young guy at work came to me and ask if I worked on cars. Was ASE certified for about 25 years, but for the last 15 I have worked on forklifts. So I haven't kept up with a lot of stuff. Keep my fleet running and work on racecars. Anyway he and his brother tried to jump start another car with his 2014 Mercedes SLK and hooked the cables backwards. Fireworks, smoke and the SLK will not come back to life. He says he has checked all the fuses and they all check good. He's watched some youtube videos and still cannot get it running. I'm thinking the ECM has given its life to protect the fuses. Have not looked at it myself yet and was wondering if my OB2 scanner will connect to this car or do they have their own super cool diagnostic tools. Just kind of hoping to learn something and maybe save the kid some money before sending to the dealership.
Thank you.
That, good sir, was funny.
Schedules haven't worked out yet but plan to go this week and check it out.
Thanks for all the input. Will let You know what I find out.
Finally got to look at this tonight and got a little more information. Seems that after the fireworks and smoke, he connected the cables up correctly and got the car to start. On the way home the battery light came on, but he managed to get home. The windows were slow to go back up and when he turned the engine off, it never started again. I checked the fuses and they are all good. The positive battery cable has some sort of "Gas charge" that will detonate and separate the cable. It is still intact. 
The negative cable has a device on it and I'm not sure how to test it, but I'm not getting any continuity between the connector pins. The cable itself has continuity from terminal to ground loop, but the three pin connector doesn't have continuity on any of the pins. Between each other or the cable itself. 
Everything in the "engine pre-fuse box" test good with an ohmmeter. And nothing looks melted or smells burnt.
