I went to my mechanic to change the oil sump filter and replace the atf oil.

I have noticed my mechanic has not heated up the oil or had much clue about how to change it. But has replaced the oil and oil sump filter.

Now I'm receiving transmission faulty message on my Idrive and the the car is not performing at its best. Does anyone have any clue on how i could fix it or if it is suitable for me to drive it like that?

 

which gearbox? Did he use the proper oil? My first port of call would be going to bmw/specialist and getting it drained and refilled properly while doing as minimal miles as possible, on my old bmw if you push the throttle to floor then turn the ignition on and hold it for 30 seconds it resets the gearbox ecu but I believe your is due to in proper service.

 

You seem to know it may not be full - so check that first.

Also what ATF did he fill it with? Lifeguard 6 or some regular ATF?

 

I have used ATF lifeguard from Meyle a German company. I have a checked it and he showerd 6 littre bottles to be empty

 

Checked the oil level was fine but the car won't start at all now, the mechanic goes one of the plugs in gearbox might be disconnected. What could be the cause?

 

If you are getting transmission fail messages, he did something wrong. There is a procedure to fill it and if you don't follow the procedure, it won't be right.

Won't start -- maybe he did more than one thing wrong.