07 A8L...I keep getting a low voltage indication in VAG on Terminal 30...sometimes as low as 10.5V. I suspect this is causing communication issues with the Auto Transmission Controller, which doesn't allow the car to start? Would like to find out what systems I can disconnect from the power source that would help me troubleshoot this circuit but still allow the car to start? I have already removed many fuses (parking brake, windshield wipers, brake controller, etc) and continue to get the low voltage indication when I read the live data. Anyone knows something about this?

My next guess is to disconnect the main supply to each fuse box to see if I read low voltage (with a meter) at each location.

 

There is a big positive connection from the battery in the rear of the car to the engine compartment that overheats. The connections in a right hand drive car are behind the carpet and insulation in the driver's footwell (to the right of accelerator) and inside a plastic box.
Not sure how this translates to a LHD car if that's what you have but would assume still on the same side as the battery, so on the LHD passenger side.
. The issue is a poor crimp of the terminal - contact resistance, overheating, undercharging and voltage drop.

 

Thank You. I will look for this. Already removed the carpet, so getting close.

 

This connection turned out to be in the same location as your right hand drive car. Mine is left hand drive, but it was on the right (passenger side) foot well. This is also the same connection where the wires come out to the starter, alternator and both radiator fans. Mine all looked good and had correct voltage.

 

Going back to the fuse box next. Plenty of corrosion found there. Hope to find a bad connection.