99 Accord Check Engine Light

My Check Engine Light came on this morning, just a few minutes after starting the car.
I checked the gas cap, don't think it is the cause.
This happened about 6 months ago, and the Honda dealer read the codes and
said I needed a new catalytic converter. I did not replace, but asked him to reset the light. (His quote was $900!)
Now, 6 months later, it is on again.
Any advice? I am suspect of the dealer, since this is a V6 and there are two converters (he didn't say which one...).
Any tips on turning off the light?
This is a 99 V6 with 135,000 highway miles. I also had a dealer replace the EGR valve at about 40,000 miles.
Thanks in advance, Kevin
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If you have an AutoZone store in your area, get them to check the code. They do this for free, using an OBDII reader that connects to a port that is probably under the middle of the drivers side of your dashboard. This will give you an accurate indication of what is causing the check engine light to come on, and you can go from there.
I believe every car sold in the US since 1996 has the same connector; 95 and earlier models have OBDI.
Kevin Lettko wrote:

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Kevin, there's probably a hundred different things that could cause your Check Engine light to come on, and I'm not exaggerating.
Stop into any AUTOZONE store, they have a meter they can connect to your car (for free) and tell you why the CE light is on -AND- they can reset it (turn it off). I would try that first. If the light doesn't come back on again after a few days then don't worry about it. However, if there really is a problem, the light will come back on again, probably somewhere in the next 100 miles or less, maybe immediately in the first mile or so. If the light does come back on again, then repairs are probably needed. Several Check Engine codes are performance-affecting and will impact your gas mileage until you get it fixed.
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What was the exact error code number? The code number will tell you which bank is setting the code.
That $900 is usual for an OEM cat. They're extremely well-made and last forever, unlike cheapie aftermarket cats. It's HIGHLY unlikely you actually need a new cat.

If the downstream O2 sensor is setting the error (which I suspect), all it means is that the ratio between upstream and downstream O2 sensors is out of range. Replacing the upstream may fix things.
A good, real-time OBD-II scanner (such as a software-based one on a laptop computer) will help a lot here. Your dealer may not have anything like that.
So what's the code?
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The dealer scanner is far more capable than any third party scanner on the market. This doesn't mean the dealer has the capability or desire to use it. If you are going to play mechanic on your OBD2 cars it is advisable to get one of the PC based programs. You could then graph the O2 sensors and determine if they are working. It will also give a lot of other information on most EPA mandated codes. Proprietary codes is another story. At 135k miles it is entirely possible a converter is getting weak and the only way to eliminate the code coming on is replace it. Also if you have two cats they usually have four sensors and the computer will run tests to compare them and also the efficiency of the converters. End result, have the codes read out as it could be something completely different...
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