Maxima Catalytic Converter

I have a 2003 Nissan Maxima with 178k on it. It recently put out a P0420 code and the mechanic said I needed to replace all 3 catalytic converters to the tune of $2500. I have already spent about $2000 on the car this year (spark plugs and something else related that I cannot recall right now) and I am not inclined to put any more money in when I had planned on selling it at the end of the year anyway. Another mechanic quoted me $550 which is certainly better, but still money that I would be throwing into an old car instead of putting toward a new one. Here are my questions - 1) how will I know when the problem absolutely has to be fixed (I have been told it could drive for months without any issues) and 2) what do I do with it if the problem hasn’t been fixed and I am ready to get rid of the car (I would never remove the MIL light bulb or anything, but I have a hard time swallowing the idea of selling it for scrap)?

The problem is an emissions problem and not a drivability problem. As long as passing an emissions test is not an issue, there is no problem in driving the car…The P0420 code is being generated by the rear oxygen sensor, not the catalytic converters. The underlying problem may indeed be a failed converter, but it’s just as likely it’s the oxygen sensor, about $100 to replace it…

Many car owners are faced with this same dilemma, as cars approach the 200K mileage plateau major, expensive repairs can be expected, be it new exhaust systems or transmissions or front ends…

Yes, it might not be the cats at all, did you ask ‘how much to replace the converter’ or ‘what’s the problem’? I’d replace the O2 sensor(s) first.

Here are other causes for P0420, besides cats:
rear O2 (oxygen) sensor is no longer working properly
exhaust leaks
damaged exhaust pipes
damaged O2 sensor wiring/connectors

I did ask what the problem was, but when the first mechanic said all three converters needed to be replaced I just told him to forget it and took the car back. The second mechanic just replaced my starter (another $200) and did not do any diagnostics on the emissions system, but did say he would replace all 3 cats for the $550. My thought after talking to the first guy was how do we know that all 3 catalytic converters are bad - couldn’t it just be one? Is there a simple way I could test it?

You have reached the point of no return. Your car is worth $2,000 or a lot less in trade-in value if it runs great and looks great. No repair unless you have a good excuse.

I think Caddy is right: it is far more likely to get the O2 sensor or maybe an exhaust leak than it is any of the three cats.
Btw, cats are a lot more expensive than 550, never mind the labor involved in removing them, labor not being free, last I checked. I bet that mechanic is going to replace your O2 sensor, your light will go off and he’ll charge you $550.

+1 @RemcoW - just the cats from Rockauto are about $550.

I’d get the rear O2 changed, see if that does it. If not, I’d look for a new(er) car.

Thanks for the advice. A new car is in the near future, I just want the Maxima to hold out until the end of the year.

This problem is not life-threatening…You can continue to drive the car. The hammer comes down when it’s emissions test time and that pesky CEL is on…

I guess if this were my car, the first thing I’d do is do ask an inde mechanic to perform a visual isnpection of the entire exhaust system. Its just a bunch of pipes, but they have to pass the exhaust gas freely from one end to the other, and most importantly for this code, not leak. It could be just that there is a small hole causing a leak, which is easily fixed. Ask your mechanic: Is the exhaust manifold bolted on with the bolts having the torque recommended? Are the connections between the pipes tight? See any visible signs of major corrosion? Feel any exhaust gas leaking out anywhere except for the end of the tailpipe?