I have a Mk4 bought in 2010 with 2.0 flexifuel engine. It's the model with the power button.
We were working with the car, when the electronics went crazy. We hardly could start the engine while pushing and pushing the button. First we thought the button crashed, but it's working right. When the car's on ignition and the engine does not run it makes a lot of failures - for instance tyre pressure sensor failure, IVDC failure, Transmission failure etc. It beeps and beeps creating a lot of failures. We keep pushing the button and, if we have luck, the engine starts. Then the car shows no failure. Every function works operational. The stopping of the engine is critical again. Today we cannot start the engine any more.
The Bosch system shows an unidentifiable failure, number U0167 and a communication-with-ECU failure number U040168.

So the start button is working, the accumulator is fine, the key works, but the car shows what I explained. We only have 3000kms in the car.

If anyone knows what is the problem with the car, please tell me.