P0420 after New cat, help please.

[Col748]

Right here goes if anyone could help with this one it would be great.

I have a 2002 yaris and the engine light came on about a month ago it was a downstream exhaust sensor heater fault, the heater circuit was open circuit in the sensor so the sensor was at fault. I replaced the downstream sensor and while I was at it I replaced the upstream sensor and the cat as well as the cat was rusting away and the hangers had rusted away to the point of snapping off. I replaced the upstream sensor as by time I'd got it out I guessed it would probably fail in a week or two anyway.

So a day after fitting the two sensors and the cat and clearing the codes the light came back on. I had a new code p0420 cat efficiency fault. Long storey short I messed about swapping old sensors about, checking for leaks, eventually putting the old cat back on with the new sensors and the light stays off.

So with the old cat and new sensors I do not get a cat code p0420.

I spoke to the supplier and they have had a concern with Japanese built yaris and new cats bringing this code on, spoke to another supplier and they have a similar concern with Japanese built yaris which this car is.

So has anyone else had this problem, how did you get round it?

I don't want to blank out the light or buy an original cat as it's £1200 just for the part.

Thanks Colin.