box100 Posted September 6, 2020 Report Share Posted September 6, 2020 I’ve been getting PO421 and PO431 CEL, on my 2005 987 the codes relate to rear O2 sensors not reading as expected. The garage fitted new Lambda sensors but no joy and tried some spacers from design911 but just got some different faults instead. The garage think I need new rear CATS and will fit if I purchase. I see a wide range of prices, but obviously don’t want to buy cheap one’s if they are rubbish. Has anyone had to purchase these before, if so link would be appreciated. Link to comment Share on other sites More sharing options...
Lonewolfgjp Posted September 6, 2020 Report Share Posted September 6, 2020 I think a pair of brand new rear cats will work out quite expensive and I’m not 100% sure you need them as they are secondary cats and the primary cats on the manifolds do most of the work. The reason I say that is a lot of the aftermarket exhausts do away with the secondary cats all together, I had a cat back system that did that and I never had any codes or failed emissions tests on the mot. As far as I know the exhaust place didn’t do any coding to allow for the lack of secondary cats. Link to comment Share on other sites More sharing options...
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