So what happens to a car when the O2 sensors go bad? just checking.
will a vag com be able to pinpoint the one thats bad?

 

without the code its anyone's guess

 

Erratic idle, lowered MPG, difficulty starting, erratic engine operation when cold.

A bad O2 should be flagged by the computer, however, I've seen intermittent O2's that don't pop up in the computer.
A VAG may help as I think it can track air/fuel mixtures and that can help detect the problem, also if can lists O2 voltages then that will
really help.

Perhaps someone with VAG experience can give you that info.

 

fault code??? guessing not allowed

 

I don't have a VAG or code list.

BTW, some Autozone stores will look up any fault codes you may have if the computer has flagged them. They should also have a list of what the code is for.

 

I have the code list and the problems incurred

 

Even if its not completely shot, its wise to replace them around 90-100k miles. Its not a part that works fine, and then just dies. They get lazy over time, and even though you may not have a CEL or fault code, that doesnt mean its operating efficiantly. I replaced my 02 sensors on my maxima at 112k miles w/no CEL or fault codes and i noticed gains in power and mpg.

 

Are you going to help him by being cryptic about it then?

 

Vagcom will list any codes, pinpoint the bad sensor and can give readouts of voltages to see if it is Dying, but hasn't tripped a code yet.

 

When one goes bad the other isn't far behind