What is the exact description of Error Code 2 ?

 

Here's what INPA gives me - unfortunately it's in German (still haven't been able to figure out how to get it into english)

 

Ignition circuit ZK1 -> Belt-tensioner driver

Do you have a picture of the new pre-tensioner you are trying?

How did the connector fit?

 

Makes sense, that's the wiring under the drivers seat that's been meddled with in the past for some reason.

So here's the connector:

and it fits in fine, my last seatbelt tensioner didn't have this connector - instead it was cut off and the two wires from the tensioner were connected to these wires:

The rest of those cables connect up to a yellow connector which fits together perfectly.

Not sure if my explination is the best, but I could take the seat out to get better pictures if that helps?

 

Was the old pretensioner detonated? Are you sure the new one has not been detonated?

There is also a connector near the charge on the pretensioner itself. That connection could be problematic - there is a safety plug in there that can break and give a code.

 

Not sure about the old one - I replaced it because it wouldn't always hold the seatbelt when I first plugged it in.

The new one is fine - I tested it with my multimeter prior to install.

The error is coming from these wires not being connected:

But I have no idea where to put these, the section of cable in the picture above is connected to the connector on the underside of my seat - there's nowhere for my tensioner to connect to these wires.

I can't figure out why someone would splice these wires, BMW provide a connector for them

 

Based on your first picture, the old pretensioner looks to not have been detonated.

You can buy the wire harness new for about $30. I have heard these can go bad.

Also, if you remove the connector from the tensioner, you can stick a zip tie in and use a multimeter to measure the resistance across the two pins. It should be around 2.1 to 2.6 ohm.

Once plugged in you can check the resistance is still similar along the wire at any point(s) easy to access going all the way back to the control module under the center console.

If it sees a short or resistance outside the normal range, it will throw a code.

 

Chase the wires back from the big yellow connector. Maybe those two wires were separated upstream to try to bypass the harness section that can go bad.

You can find threads about this harness/connector and how it goes bad. I haven't come across that specific issue yet.

You can see if the right resistance makes it all the way to the control module.