So, I've recently replaced my catalytic converter, bank 1 and 2. Both were a pretty penny (About $1,500 Each), I inspected the old catalytic converters and they look to have failed due to being clogged. I was getting P0420 & P0430 codes (Catalytic converter below efficiency).

I ran a borescope camera through one of the o2 sensor holes and noticed the cats were clogged with some type of white deposits. Definitely don't want the same thing to happen to the new cats, so i want to try and figure out what actually went wrong to cause them to clog up like this before i actually start driving the car.

Anyone know what caused them to turn out like this, and how i can go about fixing whatever issue it is?

Bank 1

Bank 1 Catalytic Converter

Bank 2

Bank 2 Catalytic Converter

  • Sometimes fuel adatives can kill a cat pay attention to what you use and make sure it is cat safe.
    – Carl
    Dec 28, 2020 at 13:15

3 Answers 3


Most cats get blocked with a combination of combustion products and burnt oil.

This happens due to two main causes:

  1. a worn engine allowing oil into the exhaust (valve seals, rings etc)

  2. the wrong oil being used - this is a common issue as people don't check for the correct grade of oil and, in many cases, opt for the cheapest.

Some cats can be cleaned but that is not always possible or easy.


The catalyst support ( the ceramic you see) breaks up because of thermal shock. This was a big problem up to about 1980 ,then better support ceramics were developed that don't breakup. I emptied about three converters in vehicles older than 1980, just remove the large Allen nut on the bottom for a couple weeks. I could no longer get on the expressway because of lost power. My guess is that your auto manufacturer hired MBAs to calculate profit,. found old cheap ceramics for your converters( they take more than 50,000 miles to pulverize and plug the converter). The MBAs probably added $ 20 to the manufactures profits. An X-ray diffraction analysis would prove my analysis but would cost more than your new converters , unless you know someone in the trade.

  • Short answer ; pulverized catalyst is plugging the catalyst bed. Dec 28, 2020 at 15:51

i guess if there was a misfire before and the car was driven for a while without fixing the misfire, then the unburnt fuel had to go to the CAT.. ignited there since it is very hot in there. With the high temps the membrane could have been melted...

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