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2011 GMC Terrain - why did my cat fail?

I have a technical question on a catalytic converter. I have a 2011 GMC Terrain with a 2.4 liter engine. At 91,000 miles the engine was diagnosed with a high oil consumption problem. It was using a quart of oil every 500 miles. GM replaced the pistons, rings, connecting rods and bearings under warranty as they issues with this engine.
shortly after the check engine light came on. Scan tool revealed a code 420 which is catalyst system low efficiency. I replaced the GM converter with an aftermarket converter and cut the GM converter open to find it clogged and caked with soot. In your opinion did the converter fail as a result of the oil consumption problem or was it due to age or mileage? Thank you. Doug Swoboda

It failed because of the oil consumption. The cat tries to convert any hydrocarbons it sees and motor oil is a hydrocarbon and it was overloaded and failed.


It was because the oil. Most people can go 250000 miles and not replace a cat as long as the car is running right .

Probably caused by the oil burning. But cats do fail even when there’s no other issue. I had to replace the converter on my wife’s 2103 Toyota at a little over 80k miles. No oil burning, no check engine light (prior to the converter cel), and no discernible misfiring. I couldn’t see anything wrong with the material in the old converter. It wasn’t melted, clogged, or loose. So I dunno. No check engine light for 30k miles after replacement though.