135i | E82 | N55 | DCT | M-Sport | DDE Trouble

[InvertedRain]

Hi everyone,

New here looking for some serious help I really messed up my daily!


The vehicle in question is a '12 BMW E82 N55 135i M-Sport in DCT at 106K.



History:

I recently got a brand new car battery that I registered with my Foxwell NT510 Elite. Everything was working correctly and I then decided to garage the car at a families members for some much needed Winter refreshing.



Previous Work / Projects:

I disconnected the battery while working on it (what I did can be found here).



Mistake:

Well I've really messed up because after reconnecting all my work back together in the engine bay I made this mistake with the car battery in flipping the wires in the attached photo of the car battery wiring.

This made the car not turn over much less start!

Freaked out especially after some time all lighting and the key fob stops responding. Had to use the key to get into the car!



Issues:

1) After realizing my mistake I flipped the wires and the car does crank but doesn't start.....


2) These are my codes in the photo attached with multiple dash warnings (engine light, service required soon, over voltage...).


3) After some time the car largely shuts down all electrical features because it thinks the battery is low?
If I disconnect and reconnect the car battery (after touching red to black to reset the car) it all works but again I only have crank but no start!



Attempts to Resolve:

1) In the fuse box diagram photo attached I've inspected all the 'DDE' fuses and all the 'Start / Stop' fuses finding no damage according to the pdf I thankfully found of N55 codes.

2) Of the fuses in the engine bay (3 of them) I found none broken down either.

3) Because I'm a new customer of MHD I also contacted them in my panic and they suggested flashing back to stock. Doing so yielded the same codes and going back and forth between stages resulted in the same codes.

4) Tried disconnecting the battery entirely touching red to black for hard reset of the entire electrical system with no success.

Clearly I've messed up something electrical and I'm at wits end because I've spent weeks prepping the car for Summer messing up at the very end.



Summary:

Disconnected and reconnected the car battery red wires incorrectly going to the car chassis itself.

Outcome of multiple electrical / engine codes. Multiple dash warnings.

Fuses appear to be okay both in the fuse box behind the glovebox and in the engine bay fuse box.

MHD tuned back to stock yields the same codes.

Car cranks over as much as I wan holding the brake pedal down but doesn't start at all.

[PRTSB1M]

I'm no electrical expert, but sounds like you fried some electronics. Based on the codes, you might try replacing all those relays and see if that clears any of the codes. Then you might need to replace the sensors that have codes showing they were shorted to B+. The car is definitely not going to start until the relay codes are resolved.

[eeghie]

sanity check (based also on the 2xx codes)
- did you verify the condition of your battery after ‘the event’. Your codes suggest their’s a problem with the battery (low voltage|short cirquit). If it’s not a real issue, erasing these codes should have solved the cranck but no ignition issue
- test the voltage drop during cranck, this should be around 0,5V. If bigger your red wire(s) might still be leaking to ground or other cable problem.

[m3_cecotto]

Hello, have you found the error already?
I understand you flipped the two red 12V wires marked in your picture?
If so i would first check the fuses in the Box above the battery. These are some very big ones like up to 250Amps or so. I think you have no voltage on the connecting point with the thinner cable.