How much should it cost to repair/replace converter in a 1999 Honda Accord LX V6?

I had the engine code P0420 come on in my 99 Accord V6. I already knew the code meant "Catalyst system efficiency below threshold," so I took it to a Honda dealership to diagnose the exact problem. They cam back to me with a write up that only said, "Catalyst system efficiency below threshold," and said the entire converter system needs to be replaced at a cost of $1,300. My car does have 120,000 miles on it and that's why they said they need to replace the whole system, convert, o2 sensors, the works. I have a feeling they never really checked the problem but just gave me the same computer readout I already had.

Okay, that all said. What is the cheapest way I can fix this. I drive this car maybe 1,000 miles / year but it still runs great I hate to dump it. But, I'm not going to pay $1,300 to have it fixed. But, I need to pass the emissions test and there's no way it will pass with this code.

So, any thoughts and/or questions.

Reposting an answer to the same sort of question from earlier today:

P0420 makes me crazy. Professional mechanics are taught it always comes from a bad catalytic converter, but in my experience it *never* comes from a bad catalytic converter. Yet, most of the time replacing the converter will make it go away for a couple of years until the new wears off and the underlying condition gets worse.

The ECU produces a P0420 code when the downstream O2 sensor (for bank 1, if dual exhaust) reports a high and fluctuating level of free oxygen where there should be a low and relatively steady level of oxygen. If the official definition was "excess oxygen in exhaust [bank 1]" nobody would make the mistake of replacing the converter. There are three general causes: an intake leak, especially in one or more branches of the manifold; a fault in the mixture control, or an exhaust leak ahead of the converter. I always start with checking for leaks. The old school way of looking for intake leaks with carburetor cleaner does not work on many modern cars, especially cars with MAP sensors (like Hondas). I like to pressurize the intake by pressing the intake duct to my face, opening the throttle, and having a helper feel and listen for leaks. With the exhaust, I duct tape a shop vac, connected to blow, onto the tail pipe and listen and feel for leaks. Mixture control is more technical. I use an oscilloscope to see what the upstream O2 sensor is saying but a five gas analyzer would be better. That makes it a job for an emissions professional.

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The cheapest place to start, if you have not been using top tier gasoline regularly (see the first source) is to either fill your mostly empty tank with top tier gasoline and change to top tier gasoline most of the time, or to put a bottle of Techron into the tank if it is mostly full, then change to top tier gasoline when you fill up from now on. It is amazing how many times that is enough to make the code go away (my daughter's has been clear for a couple years now). Otherwise, if still bad, I would bet on either an exhaust leak or a leaking intake manifold gasket. I think in 1999 Honda was still using paper gaskets that get brittle and shatter, leaking air into some cylinders and not others. The other frequent problem I see causing P0420, contaminated MAF sensors, does not apply to your Honda (it uses a MAP sensor).

The dealership's approach gives me the shivers. Although the O2 sensors typically last at least 100K miles they want to replace them because they are afraid replacing the converters will not fix it and they don't want to bring up the O2 sensors (another poor shot in the dark) after their first try failed. I suppose that the 20+ year life expectancy of the converter does not bother them, either, but why should the customer pay more because the shop is not confident of their diagnosis?

Go somewhere else. Not Honda. Cheapest part you can get for such an old car.