Is code O0420 (Cat system efficiency below threshold) casued by excessive oil comsuption?

I have a Toyota corolla 2002 with 82,700 miles on it. On July 28th, I had my car fixed, the problem is “…Excessive oil usage. Oil consumption test showed 1/2 quart per 400 miles traveled. Internals show excessive carbon burning oil on piston tops and valves. Oil control rings build up with excessive oil. Replaced short block, machined head, replaced all lower end gaskets…”. Two days ago, my check engine light is on, and the diagnosis is “Code O0420 : Catalyst system efficiency below threshold (Bank #1)”.

My questions is whether the Catalyst problem is caused by the oil consumption problem which was fixed in July. If yes, my dealer will cover this, otherwise I need pay for this.


, my car had a engine problem “”, onsider myself very conscious about the mileage I get. Here is my story. I was getting 29-31 mi/gallon mixed highway and city driving and I was kind of concerned. Then, I changed my original Denso spark plugs (iridium) with Bosch (Platinum) and my fuel economy went down to 23 mi/g. I heard from my friend that if you change the spark plugs then you need to reset the computer so that it can readjust the air-fuel ratio as per the plug design conditions. I didn?t like the new plugs so, I cleaned the old plugs as they were looking ok and I got my mileage back to 29-30 (I had also reset the computer this time). I wasn?t still happy with the mileage so I researched and cleaned MAF sensor with Electronic Part Cleaner. I drove about 400 miles without any problems. Then, on next gas filling about 60-70% of my driving was in the city (about 170), and after a trip of about 100 miles on freeway check engine light came on. I didn?t check the code and disconnected the battery to get rid of engine lights. I drove like 500 miles without any problems (city as well as freeway) and then check engine light came on freeway driving. This time I checked the error codes with a scanner and it shows the following conditions:

Code P0420 : Catalyst system efficiency below threshold (Bank #1)

Speed 60 mi/hr

RPM 2906

Engine Load 30.6%

Temperature 189 (F I guess)

Fuel Pressure -5.5 -3.1 psi

To answer your question, YES, it’s highly likely that the catalytic converter failed due to all the oil going through the exhaust system. Catalytic converters get clogged when an engine is burning oil.

A quart in 800 miles is WAY excessive for a Corolla, especially at this mileage. Who paid for this repair work? I hope it was Toyota.

What’s with the second half of your post? It has nothing to do with the first half.