VW catalytic converter

I bought a 2001 vw GTI in March of 2007. Recently my engine light came on and my mechanic said I would have to replace the catalytic converter (code P0420)@ $1,100.00. Since purchasing the car I have had to replace spark plugs and wires, oxygen sensors and repair a coolant leak near the engine. I know that these problems relate to each other but I don’t know how they relate. Can someone please explain what might have caused this domino effect? Should I be looking at anything else? My mechanic said the engine was sound when I first bought the car and it has never run hot.

How do you know "that these problems relate to each other"  I suspect they don't.  Plugs, wires and even oxygen sensors are consider maintenance (like oil changes), not repairs. They are part of the cost of ownership, just like gas. 

The O? sensor may be related to the converter, and maybe even the plugs, but only if they have been ignored long enough to damage the converter.

BTW that price seems high to me for a converter. You can get an after market converter for much less the OEM and usually the labor to replace one is not all that high. Are you sure it really needs one? I don’t recall what the code means, maybe someone else here does, but as a general rule you don’t replace an expensive part because of a code. Codes relate to some measurement that is outside the norm. Usually there are more than one possible cause.

Good Luck

Maybe I wasn’t explaining my question well. I know “that these problems relate to each other” because when I researched catalytic converter problems online many posts have cited oxygen sensors, coolant leaks etc. as the reason for the code P0420.

You can read a bit more about this code at this webpage if you like: http://www…bank-1.php.

Since all the work done on my car in the last 6 months touches on the one of the possible causes of this code I was hoping someone could explain to me what might have happened.

I do agree with you that wires and plugs can be considered maintenance, but I think it’s safe to say that replacement of a catalytic converter after 85,000 miles is out of the ordinary and I thought it would be prudent to investigate it further.


Well, if the vehicle had the original plugs in it then those could have knocked out the wires and even ruined the converter.
Coolant leaking into the combustion chambers can kill oxygen sensors and ruin converters but from your description the coolant leak sounds like an external one. If so, this has no affect on the O2s or the converters.

There are tests to determine if combustion gasses are entering the cooling system.
You state the car has never run hot, but that’s only on your watch. You just bought the vehicle in 3/07 and there was a lot of water under the bridge between when the car was first sold and that date.

If your mechanic is replacing plugs it is his responsibility to not just replace them but examine the tips for any abnormalties. JMHO, but a compression test should always be performed when the plugs are out, and especially if the vehicle mileage is around a 100k miles or more.

As mentioned by Mr. Meehan, price the converter around. You should be able to find a cheaper aftermarket converter for much less. That’s also assuming the converter is actually bad.

Thanks for the info. I have a feeling the prior owner did not take good care of the car. I got a good deal on it when a dealership declared bankrupcy. Of course the engine light came on as I was driving it home. There are no lemon laws in KY so I knew I was taking a gamble.

My mechanic never said anything about the plug tips and I didn’t know enough to ask.

Are there any tests I should ask him to perform? Is there anything else I should be asking?

I’ll look into those aftermarket converters. I actually do trust my mechanic and I’m sure he would help me find one if I asked. Are there any negatives to aftermarket converters?

This doesn’t really answer your question, but… VW has extended it’s emissions warranty, which covers replacement of the catalytic converter, on certain cars. As of Oct 2005 the extension included 1999-2001 vehicles, and in 2007 some '02 vehicles were added to that… My wife received notice in mid-Summer '07 about this regarding her '02 Golf (80k miles on it), and a week later the converter crapped out and was replaced free of charge. It might be worth it to see if your '01 GTI is covered by this extended warranty as well.