I've had an intermittent CEL over the last year or so.

Kept getting P0420/P0430 “Converter efficiency below threshold.”

Started to happen every 500 miles or so and got progressively worse. Till it was happening every 100 miles or so.

A month ago I found out I was losing coolant due to bad radiators.
I've put 1000 miles on the car since then with no CEL.

It looks like the coolant was getting down to the cats and burning off.

Doesn't look like it was my after-market exhaust at all.

 

Happy the problem is fixed but how did the coolant get from rads to cats= good distance..

 

I also replaced the coolant expansion tank at the same time for preventative measure. I suspect it might have been the coolant tank rather than the radiators as that's a long way for coolant to leak.

I know I dripped a bit the few times I topped off, which would explain the increased frequency of the codes over the last few months.

Just glad that it finally appears to be resolved.

Definitely shows the need for investigation rather than jumping to conclusions about the cats.

 

closest route would be the expansion tank breather overflow spilling onto them lol was there white residue on the cats or pipes at all? that would be odd. i get patches sometime on the my motor mounts from a drip or two and thats the source of it.