P0153: I was told that this is the bank 2 sensor 1 o2 sensor that needs to be replaced. Is that correct?
P0118: coolant temp sensor?
P0422 Main Catalyst Below Threshold (Bank 1): I am not sure what this one means?
this is on a 1999 a6 2.8q auto

 

If I had to guess all 3 could be because of 1 code. Either o2 or temp. O2 would be easiest so I'd replace it. The clear a go from there

 

Wouldnt it be easier to replace the temp sensor just because it is easier to get to? It is also a fraction of the price of an o2 sensor. Or do you think it is most likely the o2 sensor thats causing the check engine light?

 

I think it's more likely the o2. Vag the car and see what each are doing

 

The problem is that I dont have a VAG, my brother has a scanner that I have been using. I was thinking about getting a VAG but then I don't have a laptop lol.... 3 computers in the house and they are all desktops. I guess that I will have to replace both sensors, the car has 150k on it so they would probably need to be replaced anyways..

 

Find someone with vag near you. Duh.

I've sold a couple laptops on c-list. See if there's any cheap ones for sale

 

About the temp sensors, I have noticed that there are two different kinds being sold. One that has a more square looking connection and one with the round looking connection. I will need the more square looking one, correct?

 

Check yours and see. I'm a b5 guy

 

Pre-cat and post-cat O2 sensors are different part # ... the pre-cat one does lots more than the post-cat one, so better be OEM, while the post-cat one can be generic among postings. Also go with the ones that match your engine code.

You can check out some info (P0421, P0431) from : O2 Simulator, mini catalytic Converter cel fix

 

I have actually replaced an o2 sensor on my old 1999 a4 b5 2.8q with a universal one and and it worked out great. It was bank 1 sensor 1, so basically the same thing as bank 2 sensor 1. I really don't see any difference between OEM and universal other than having to rewire the universal sensor which I don't mind.