Hey everyone. 

Im new to the forum and to Audi's in general so i apologise in advance if what im saying has been mentioned before.

Iv recently purchased a 2006 8P A3 with a 2.0 FSI petrol. I got it cheap with some jobs needing doing to it. Im located in New Zealand, this car was a japanese import(yes a bit odd). And it came with a japanese head unit that was useless. After i had the car mostly sorted and ready to go i thought id throw a new head unit in. I then found that the japanese head unit had about 20 kilometres of extra wiring added to the original loom. Stupidity i left the ignition on for the hours i spent untangling the mess. And when i finally had it working and went to start the car i got a battery warning light and a very slow crank. Iv only ever driven "older" more basic japanese cars and 4x4's so i instinctively hooked some jump leads on and fired the a3 up. To which i was met with a engine light, power steering light and a esp light. I plugged in my cheap obd2 scanner to find the fault saying "lost communication with tcm" i cleared the code and found that the other 2 lights might just need a drive to sort themselves out. So i went to go for a drive. But, the car is stuck in park. I found the emergency release, and once released the car goes into gear but with a sizeable clunk. Iv spent hours checking every fuse in the engine bay and the dash but nothing was blown. Im totally stumped now. Is it possible that iv done some serious damage to the TCM or could there be another fuse box that i could check? 

Any help at all would be really appreciated. Auto electricians aren't cheap so im doing my best to try avoid it.

Thanks in advance

I doubt it was the jump start that caused the problem. My guesses are:

[1] the head unit you removed was integral to the ECU. Can you refit it to test?

[2] the 12 volt battery is dying. How old is it?

Battery seems fine. Holding 12.5 volts and starts the car good. The old head unit idea sounds promising. Ill give that a go. Thanks for the tip.

Forget the voltage of the battery. The right voltage and the ability to start the engine do not mean it is in good condition. Internal faults can interfere with the car's electronics and cause false warning messages and symptoms such as limp mode, loss of radio presets, loss of cruise control etc. So I ask again how old is the battery?

It is pretty new. About a year old. 

Fair enough, then it must be something else unless damaged by draining it flat.

I did have the lights set to auto, so the lights were most likely on for a while. Iv been through everything again. Found something that rekoned by holding the accelerator flat for 20 seconds re calibrates or resets the DSG. Tried that to no avail. 

Looks like you need an electrician.

Just re installed the old head unit. Unfortunately no change.

You definitely need an auto electrician or Audi independent specialist. 

Just pulled the TCM or TCU whichever you want to call it, from the left front wheel arch. All the connections look ok. I checked the plug and there is power getting to it. So that sort of rules out any blown fuses maybe. Will blast it all with contact cleaner. Otherwise my next options are see a expert or buy a new TCM which is about 300NZD or 150 pounds. Just trying to keep the thread going for anyone in future if they have the same issue.

Side note if anyone has the wiring diagram for the plug id really appreciate it if they could send it through. Would help to see if any particular contacts should have power

Cheers

Glad you've found it's getting power, keep us posted on how you get on cleaning the tcm. 

Just pulled the cover off the module, everything looks in decent order, no fried bits. Gave everything a thorough blast with contact cleaner. Put it back together and plugged it back in. And sadly nothing. 

I decided to order a new TCM. installed it and NOTHING. really am stumped. Out of desperation i remembered one ground i pulled out with the old head unit which i didn't plug back in as the unit turned on without it. it was located close to the CAN bus so thought there might be so correlation. Sadly nothing still. Currently i have the glove box out in an effort to find anything that i may have touched when fiddling with the head unit. the one thing that pops out is a stray plug which i have no recollection pulling out and doesn't fit any of the head unit wiring. Ill attach a photo in a separate reply.