I did my first oil change on my own for this car, and I think I did the steps as suggested by various people on this forum, using dieselgiant as my main guide. While taking off the canister cover, I tried to make doubly extra careful not to disturb any of the connections, especially on the driver's side of the canister.

But alas, while struggling to get it off, one of them did disconnect. Right next to the driver's side bolt there are three wires bundled together, a red one, a green one, and one that connects to a whitish plastic thing. It was the latter one that disconnected, but I put it back together immediately.

I hoped everything would be fine.

Then after finishing the oil change I went out for a test drive, and everything felt smooth, the engine, the shifting, the starting, the door locks...

I stopped the car to clear the garage, and started it up again to park it inside, and for some reason, the shifting was harder than it had ever been. Going from park to reverse, and from reverse to drive-- both were so hard the car lurched backward (or forward).

Could this be because of the problem with disconnection I had while changing oil? I checked and checked and nothing else looks like it came loose. Is there something I forgot to do?

Edit: Also, when I shut the car off, key at position 1 (or is it 0? whatever the lowest position is), I hear a humming in the rear of the car that goes on for several seconds. It eventually stops. Is this a related problem?