Catalytic converter replacement

Hi! My 2003 Mazda MPV had its engine light go on, and stay on for several days (however, the light went out while driving to the mechanic’s, of course!). The mechanic told me the diagnostics showed that the catalytic converter is failing. I have approximately three months left (failing inspection in April; two months temporary sticker). My question is: I was quoted a price of $1700 - $1800 for repair. As my husband and I are financially bereft at this point in time, should I go for the repair and hope I get another year or two out of the van? Or is it too risky and should I just say forget about it and purchase a used vehicle? Please advise. Thank you so much.

That’s all that’s wrong with it and you’re considering replacing it with a used vehicle with an unknown past? Are you crazy?

Seriously, take it to an independantly owned and operated shop and get it verified. It may be just the oxygen sensor. And it it does need a cat, an independant shop should cut that bill by half with an OEM replacement converter.

Thank you for responding. The van does have quite noticeable rusting. The mechanic I brought it to is the same independently owned garage I’ve been bringing it to for years, and they generally do good work. I posted twice before, but I am new to this website and I don’t think my posts ever showed, because I never received a single response. So by this third posting, I omitted the rust issue by accident. I would prefer to have it replaced. But when I asked my mechanic if he thought we could get another year or two out of the van his response was along the lines of “Well, it’s like geriatric medicine. You know, you could sit in a chair all day and do nothing and be fine, or you could have a heart attack at any moment. I really don’t want to tell you that you will get another year or two out of it, because something else could go wrong.”. Now, due to a job loss, my husband and I are also losing our home. We are really financially shaky right now. So, I would rather have the van fixed and continue driving it than purchase, as you said, a used vehicle with an unknown past. But I was also wondering if I was being overcharged. I live in NH…know any reputable mechanics in southern NH or northern MA?! Thank you so much for your help. It is appreciated. I am sorry that not all of us are mechanically savvy about cars. :frowning:

Good Lord, you have absolutely nothing to apologize for. Nobody is an expert in everything.

I think you should definitely repair it. It isn’t the type of failure that suggests that the vehicle is worn out. It’s a normal failure of a part that eventually needs replacement on most vehicles when they get old. It does not spell impending doom, and it isn’t something that will cause anything else to fail or deteriorate. Occasionally an older vehicle will need something fixed. That’s all this is. A normal sign of an aging vehicle.

I too live in southern NH and I wish I knew of a reputable shop…but unfortunately I don’t. I used to, but they’ve changed these past years. Sorry. Mike lives in southern NH too. Perhaps he knows of one. Mike?

We could give better advice if you could post the code you are getting. Ask you mechanic what the code was. It will be an a form of the letter P followed by four numbers, like P0420. It would also be helpful to know the number of miles on the vehicle. For example, if it is P0420 and you have between 100 and 120k on the vehicle, I would more likely suspect the rear O2 sensor than the catalytic converter, even though that code says that the cat efficiency is below threshold.

A Rockauto cats range from $134 to $345. Don’t know which or how many are on there or which is supposedly bad but as Keith said, need the codes first.

Thank you all kindly for your help. I just spoke with the mechanic who told me the code was P0421 and I believe the van is approaching 140k miles. The mechanic told me that he used to see this code about twice a year, but that ever since they started using ethanol in the fuel, he now sees it about twice a week. He said the heat from the alcohol burn off eats the part right up. I have no idea if this makes sense to you guys? He also said the price would be $1684.77 (not sure if that includes labor or not; I forgot to ask) and that would be for an original. He told me the aftermarket cc parts have a finite life span and if he put one in I’d probably be back within a few months. What do you think about all this? Again, thank you for your input. I truly appreciate your help.

Mechanic? Why not try a muffler shop. They work on exhaust all day. They can explain oem and aftermarket cat choices. If your car is running ok, than a replacement cat will last a long time.

This is the same as a P0420, its just that the warm up cat is monitored instead of the rear cat. These can be a little pricy as they are often built into the exhaust manifold. again, I would consider replacing the rear O2 sensor before replacing the Cat.

Your mechanic is partially correct about the aftermarket cats, some are good, some not so much, but usually even the not so good ones will still last two to three years, but discuss the O2 sensor with him and ask him if you pay all this much for a new cat and it doesn’t fix the problem, will he keep you old cat and put it back on, refund your money and then do the rear O2 sensor?

To determine weather it is the O2 sensor or the cat, he would need a dual trace Oscilloscope or a specialty meter. If he doesn’t have these, then he is just guessing and guessing in favor of an O2 sensor is a lot less expensive and works more often than a new cat. We see this all the time when someone posts in that they have spent thousands on a new cat only to not have it fix this code and they want to know what to do next.

BTW, the computer is not actually checking the cat, it is comparing the outputs of the front and rear O2 sensors. Those sensors are also monitored under different tests with their own codes, but they can still pass their own tests, but the rear sensor can have an issue that makes it look like the cat is bad when it is the rear sensor instead.

One other source of this code is a leak in the exhaust system. You mentioned a lot of rust so if the exhaust has a hole in it any where before the rear O2 sensor, or a leaking gasket, you will also get this code.

BTW, you have two warmup cats, I just checked, they are built into the exhaust manifold and you have a V6 engine, so you have two exhaust manifolds. There is only one rear cat and if your mechanic is looking at this one, he is way off. The code is only for the bank 1 cat, after market cats run about $400 each, was he looking at replacing both?

One more thing, none of the aftermarket cats that I looked at are certified for sale in California. That could be because they don’t meet the standards for the OEM cat or it could simply mean that they have never applied to CARB (California Air Resources Board) for certification because of cost vs sales potential.


I believe cars with California emissions legally need to fixed using CARB approved emissions parts, even if the car is not registered in California.

Make absolutely sure any parts that are installed are “approved”

db4690, that is not quite accurate, but there is merit in your statement. There are some states, 7 I believe but I don’t know which ones, that require any replacement parts to be approved by CARB. You might live in one of those states.