Lost Communication with tcm after jump start

[dannyanny246]

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

[cliffcoggin]

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?

[dannyanny246]

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.

[cliffcoggin]

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?

[dannyanny246]

It is pretty new. About a year old. 

[cliffcoggin]

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

[dannyanny246]

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.