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Catalytic converter

Hi! I own a 2002 Grand Prix. I’ve enjoyed the car very much. About 2 yrs ago I replaced my catalytic converter. Since then, approximately every few months something is causing the converter to need to be replaced. It was under warranty but now it’s getting tiresome. What is causing this to happen?

We need more information. Who’s diagnosing a faulty catalytic converter every few months, and on what is the diagnosis based?

Does the “check engine” light come on? If so, what trouble codes are stored in the computer?

It’s EXTREMELY unusual to need a new catalytic converter more than once in a car’s life. Every few months is a sign of something drastically wrong.

I’m going to assume that this has to do with a “check engine light” code. I’ll go out on a limb and assume the code is P0420 - although you should find out what the exact error code is and post it.

Its true that there are codes that will be set if the converter is bad. But its also the case that computer never actually knows anything at all about the converter itself. It reports about this kind of thing only on readings about the exhaust it is getting from oxygen sensors.

The info from the sensors can be unreliable because of sensor or wiring problems. The actual content of the exhaust can be off for reasons that have nothing to do with the converter (e.g. exhaust leaks).

It is also possible that the car is having some other issue that is continually contaminating the converter. It seems that it may be time to have someone else take a look at the car.

I’ve had more than one mechanic work on my car. The converter is actually needing replacing. No doubt about it. I’m wondering if there’s something mechanically that could be causing these parts to go prematurely. I hate to sell my car because of this.

I’m curious as to how you know that the converter actually needs to be replaced. Describe the mode of failure.

Actual converter failures often come from engine problems - fuel, oil or antifreeze entering the exhaust will do it. So I don’t know that you’d say its “mechanical” - some of it can be (e.g. worn oil rings allowing excess oil into the combustion chambers). Some of its wouldn’t be (e.g. improper fuel mix allowing unburned fuel into to the exhaust, although that could be mechanical or electronic).

The place to start is with the exact failure mode of the prior converters. This is one more reason that someone else ought to be looking at the car. It seems liklely that whomever is just putting new cats on it isn’t paying attention.

Thanks so much. The 2 dx codes that came up are p0420 and p0463. CAT LOW BANK 1 and FUEL PUMP. Is it possible that the fuel pump is responsible also for the CC code to also appear? I really appreciate your input.

The P0420 is the one that doesn’t actually tell you anything about the cat directly. All the computer knows is that the readings from the O2 sensor before the cat & the O2 sensor after the cat are too similar. If a) the O2 sensors & their circuits are in correct working order and if b) the cat is doing its job then the two readings should be quite different. So hopefully your certainty about the cats being bad is based on more than just that code. Problems with those O2 sensors, or with their circuits, or exhaust leaks can also throw the code even when the cat is fine.

I am not all that familiar with the P0463 but I think its only about the fuel level sensor in the fuel tank. I don’t know what, if anything, a problem there would do. However, you need to have someone check the stuff above and also find out whether you might be running too rich (too much fuel), burning too much oil, or spitting antifreeze through your exhaust.

A bad downstream O2 sensor could be giving a wrong reading to the ECU causing it to set a code related to the catalytic converter. The purpose of the downstream O2 sensor is to detect whether the catalytic converter is doing it’s job properly or not. If the downstream 02 sensor is old I’d invest in buying a new sensor and installing it before replacing the catalytic converter again. I know O2 sensors can be fairly expensive from an auto parts store and you don’t want to spend money unnecessarily, but I recently bought an O2 sensor for my '02 Ford Escort off eBay, the buy it now price was $20. or best offer. I offered them $18. and got a new direct fit sensor that would have otherwise cost about $60-$80 at the local auto parts store. I’d suggest going to eBay and do a search for 2002 Pontiac Grand Prix oxygen sensor and see what kind of deal I could get on one there. If you can turn a wrench you can probably change the O2 sensor yourself in a few minutes, but if you change it yourself be sure to put some anti seize on the threads of the new sensor in case it ever has to be changed again it won’t be seized into the pipe making it very difficult to remove.

Is your car overheating? Or, is it burning oil? Either of these could be related to something that would “poison” the catalytic converter. The P0420 code can also be related to an exhaust system leak - maybe you have a leak somewhere? Or as FordMan said, it could be a sensor issue. It takes a certain number of cycles for the check engine light to come on after being reset, so it may be that after the cat is replaced and the check engine light is reset, that the couple of months is just the time necessary to get the codes to appear again. In other words, maybe the catalytic converter replacement is not actually fixing the problem. If your mechanic just resets the check engine light, how long does it take for it to come on again? That could tell you something.