[charleskeyz]

So… here in Denver, the temperature has gotten much colder the past few weeks. I had a battery icon pop up on my dash 2-3 times in the same week. I figured , I have owned my 2011 328i X drive (n51) for over two years now… it would be a good time to possibly replace the battery.

Long story short, I installed the battery backwards and caused some damage. The headlights came on when the keys weren’t even in the car, so I knew something was wrong. It sounded like a secondary air pump was going possibly. I hopped in, tried to start it. It didn’t start, I smelled somthing burning… took the keys out.

Now that I have overcome the shame and worked up the courage to ask for help, I am here.

I went back and installed the battery correctly. Tried to start it. It cranked, but no start. It was cold, went home.

The next day, same thing. So I grab a pulse trickle charger and hook it to the battery and pop open the fuse box behind the glove box.

The fuse box is in such an awkward place that it’s hard to get a decent vantage point for some of the deeper fuses.

Good news, I found a fuel pump fuse that was toast. Only one I’ve found blown so far. You can tell this box took some current, many of the fuses are a bit burnt on the metal, but still good.

I noticed quite a bit of fuses seemed to be missing, so I purchased a fuse kit. (Large, regular, mini, micro sizes.. and started changing out fuses.

So now I don’t know what I mixed up, but now it won’t even crank. I’m pretty sure I put a fuse back in the wrong spot.

I’m assuming I probably have a fried alternator or starter or somthing. I am prepared to do what I have to do. It’s my daily driver so it’s not optional.

What do I do now?

[e90yyc]

Scan for codes. There will probably be a ridiculous amount, so clear them and then see what comes back. Know that some may be red herrings; electrical issues can be challenging to diagnose.

Possible you’ve fried a few modules, but it’s hard to say. For instance, the FRM is known for being a little bitch of a module even when hooked up with correct polarity; failures have occurred just from disconnecting and reconnecting a battery for very normal work.

I know we all have to learn somehow and in the process we sometimes fuck things up. Good on you for asking for help.

With that said, how would you rank your abilities either with cars in general or this platform specifically? I ask simply because while there are surely things you can do to resolve this, you may want to get help from a trusted mechanic on this one. (Your comment about missing fuses has me concerned, to be honest…)

Check alternator diodes. They are probably toast but I like to have evidence of failure before I just replace parts. Good multimeters will have a diode test function. They are soldered to the diode bridge and aren’t (afaik) replaceable if they’re fucked. So, likely a new alternator is in order. I wouldn’t put anything less than reman OE in. Don’t go to Pep Boys.

Use your nose to track down anything that smells funny and could indicate burnt wiring or other problems. Ultimately this will be an iterative process, so start with codes.

[Efthreeoh]

I have to ask how did you even do that? If you had the correct battery, putting it in backwards where the terminals were (-) towards the front of the car and the (+) battery post at the rear of the car, both posts would be on the trunk side of the battery instead of on the fender side of the battery. I don't see how the cables would fit, there is not enough slack in the cables, especially the red positive BST on the (+) battery post.

[eastsidaz]

Originally Posted by Efthreeoh

I have to ask how did you even do that? If you had the correct battery, putting it in backwards where the terminals were (-) towards the front of the car and the (+) battery post at the rear of the car, both posts would be on the trunk side of the battery instead of on the fender side of the battery. I don't see how the cables would fit, there is not enough slack in the cables, especially the red positive BST on the (+) battery post.

That's what I was thinking. Not sure if it's even possible.

[Efthreeoh]

Originally Posted by eastsidaz

That's what I was thinking. Not sure if it's even possible.

I've done 4 battery replacements in my E90 and one for a friend with an E90, so I know the battery hook up pretty well. Using the correct battery type for the E90, I just don't see how the cables would fit, they are just not long enough. Unless the OP's E90 has been totally hacked with aftermarket cables and has no BST and no IBS (the US market 328i should have both depending on equipment level), it could be possible, but the car would be holding all kinds of codes.