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At the last MOT the Polo got through after some issues around emissions. A new rear O2 sensor was fitted. Also, I was advised that the cat was on the way out. Would this most likely be the front cat or the one under the body?

While I was driving a few months ago I heard the sound of something hitting metal. I stopped at the roadside and found what looks like a heat shield/guard of a cat. When I later looked under the vehicle, cat is just a smooth metal casing as per photo below.

I'm wondering if the heat shield/guard fell off the Polo or if I just drove over one that had fallen onto the road.

Is a heat shield/guard fitted to the Polo underbody cat?

I seem to remember that VW Group cars tend to have heat shielding fitted to the bodywork - in the early days cars tended to have a heat shield on the cat though.

So, which cat is on the way out, at a guess I'd think that it would be the manucat, ie the first one that forms part of the manifold, but that is purely a guess, other than checking the running temperature on the casing, I'm not sure that anyone could point out which cat was underperforming - though you would need to have a reliable figure for the running temperature of both when working correctly at a known ambient temperature etc.

I seem to remember there being some kind of cat efficiency monitoring in VAGCOM.

It might be easy to get an IR thermometer on the mancat in/out (after removing the shield) and check the temp diff. Not so easy underbody but if I can confirm the mancat temp differential that might be enough.

littlepolo wrote: Fri Sep 25, 2020 10:36 am I seem to remember there being some kind of cat efficiency monitoring in VAGCOM.

It might be easy to get an IR thermometer on the mancat in/out (after removing the shield) and check the temp diff. Not so easy underbody but if I can confirm the mancat temp differential that might be enough.

Yes, there is. Can't remember the exact basic setting but it doesn't seem to tell you much it passed the cat on my 02' 1.2 which then failed MOT for carbon monoxide.

You can get a "catalyst temperature" field in measured values block 034 I believe but I don't know which cat that would monitor or how accurate it is. If I had to guess it would probably be the first cat.

So I recollect. When I had emissions problems before I investigated but could not find anything helpful.

I guess that is the first cat. Might be worth a look.

Do these look familiar?

Would a missing shield be an MOT fail?