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Catalytic converter - twice in a year?

Hi all, I have an 05 GTI I with around 87k miles on it. A few months after I bought it the cat went. Dealer replaced it, all good. Now (11months later) the car is in the shop because the check engine light is on and it turns out I need a new cat. Again. Dealer will cover the part, and I pay labor. Has anyone had this experience? Is it symptomatic of a larger problem?

There’s three ways a catalytic converter is damaged. Physical damage, thermal shock, or contamination.

If there’s no physical damage or thermal shock damage where the subtrate is broken/melted, then the cat must be getting contaminated. And for that you look at operation of the engine.


rich fuel mixture from a bad O2 and or radiator fluid from a head leak can cause is. Lazy O2 sensors may not trip a fault.


First of all, that P0420 catalyst efficiency code does not necessarily mean the cat is bad

faulty oxygen sensors could also cause the code

exhaust leaks upstream of the sensors are a factor

Sometimes the PCM software simply needs an update

Assuming the cat is indeed bad, here are some things that can cause it

Excessive oil consumption
leaking fuel injectors

Thank you so much for the comments! Do you think the dealer is just replacing the entire cat because it’s “easier”? Should I have my mechanic check for they other issues mentioned?


Definitely have somebody see if there’s an underlying reason why you’re going through cats so quickly

Do you use much oil?