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1999 Honda Accord LX ULEV Catalytic Converter options

Hello all,

For the past several months I have been hearing a rattling sound coming from underneath my car when in “Drive” before parking or at very low speeds. I brought it in to my local mechanic and he stated that it is the catalytic converter. So far the check engine light has not come on, but the sound has become progressively worse. He quoted me a price of $350 for parts and labor but later told me that because it is a ULEV (Ultra Low Emissions Vehicle), that that catalytic would not be sufficient. He later spoke to Honda and told me it would be $1100.00. From what I have seen online that is right in the ballpark for a new cat on a ULEV Honda Accord. Does anyone know if a cheaper catalytic converter can be used while still passing emissions testing?

I forgot to add that the mechanic did attempt to compress the catalytic converter with a large “clamp” in order to stop the rattling noise. It was a cheap fix and the sound only went away for a day or 2, only to return just as before.

If the Check Engine light isn’t on there’s nothing wrong with the catalytic converter.

Take the car to another shop and ask if they could check for a loose heat shield.


Thanks for your quick reply. If it is the heat shield, does it make sense that the rattling sound only manifests itself when in "drive’ and not when in “park”? I have only noticed it when at very slow speeds before parking etc (and sometimes even in Reverse), but maybe at higher speeds i don’t just hear it over the road noise.

I hope that the mechanic didn’t damage my catalytic converter if it wasn’t faulty.

If you don’t live in California, finding a cheaper converter should not be an issue. If you do, then probably the Honda part is your best bet. In Cali the replacement must meet or exceed the original emissions. It doesn’t matter if even an inferior replacement part makes your car cleaner than 99% of all other vehicles on the road.

But I’d expect to see the CEL lit if the converter was shot. You should go ahead and get the car inspected at a state inspection site and see if it passes before you buy a new converter. If it fails, get the part replaced with the genuine overpriced Honda part, but if it passes, replace the mechanic.

The heat shield as stated above seems most reasonable. I had my great muffler guy who actually welded a split catalytic converter for 10 bucks vs replacement. The car did not fail emissions test. Conclusion, you have options, check them out!

I actually bought the car used in California (probably why it is a ULEV), but am currently living in Wisconsin. I think I am due for emissions testing this year so I will take your advice. Thanks much.

Heat shield rattles depend on where exactly they’re broken for what frequency of vibration will set them off. Some will rattle with the car in park at idle, some with it in drive at idle (engine is at a different RPM then), and some will rattle when the car is moving at certain speeds in certain gears.

At any rate, I’d bet a lot of money that what you have is a bad heat shield and your mechanic wants to buy something expensive with your money. Find a different mechanic, have him fix the heat shield, and don’t worry about replacing the cat.

If the unlikely happens and it really is a bad cat, you can get a direct OE replacement for your car from Catco for $170. $1100 for a cat is highway robbery.

In Wisconsin, if you actually DO need a new converter (I doubt it), an aftemarket replacement should be fine.
Here’s one site that should be able to find a fit for your car:

I think it’s just a rattle due to something that is loose or broken, as Shadowfax wrote, a heat shield or another part of the exhaust. Catalytic converters are pretty sturdy in terms of rot and rust compared to the rest of the exhaust system.

Are you getting some kind of break in the registration fee because the car is ULEV? Can you move the car out of the ULEV catagorey, get a normal cat. and pay normal license fees?

Looks like my last post didn’t actually post. I haven’t looked into the possibility of getting a break on registration fees but I’ll check it out. Thank you all for the help!

A little backwards from what I meant. I would think you would be paying less for registration because your car meets ULEV standards (which I was suprised to hear even existed in 1999). What benifit is it to you to own a car that meets or must meet ULEV standards?. I can’t see registration for a 1999 moving all that much lower than it is going to get. In other words, why do you own a ULEV car if it so expensive to maintain at ULEV standards, there has to be a trade off that benefits you in some way.

When the heat shield on my 97 Taurus broke (road debris), it rattled only during acceleration from a stop - the engine torque / vehicle speed had to be in a very specific range to set it off.

I bent it back into shape, drilled a new hole, bolted on a stainless steel strap and bolted that back to the body, replacing the bolt that had torn out. $5 in parts and the problem was fixed.

The same day I fixed it, I pulled alongside a mid-90s Honda Accord that had the EXACT same rattle sound that I had, only in their case it happened only at idle.

From my experience, these seem to be fairly common occurances on Hondas and Fords. I don’t personally know anyone who has had one for over 10 years without needing some sort of repair on their heat shields - but in all cases the cost has been under $30, even professionally done. In some cases, the mechanics even refused to charge for the repair it was so easy…

Very good point ‘oldschool’. To tell you the truth, when I bought the car used about 6 or 7 years ago, I didn’t realize that the ULEV standards would be so expensive to maintain. I needed a car and got a Honda because of reliability. The joke’s on me.
I have definitely learned my lesson with the high maintenance costs of this car.

This morning I spoke to the mechanic that diagnosed the rattling catalytic converter. He stated that it would require a Honda Catalytic converter (new) replacement because as a ULEV, the oxygen sensors on the vehicle’s computer system might not recognize a cat other than the original. Does this make any sense?

I asked him about the heat shield and he said that is the first thing he looked for but didn’t see any issues with it being loose etc.

I suppose I will just wait and see what happens.

I would think the problem would more likely be with a check engine light that gets turned on because the results of the work the cat. is doing is outside the parameters the ECU is programed to expect to see. Now we are getting into a real "perhaps’ and "maybe’ status. Perhaps the ECU can be flashed with a non ULEV program and maybe that will keep the light from comming on. It will take a person who has turned a ULEV car into a “standard” emission level car to help here, or we will be breaking new ground,all on your dime.We certainly can make best guesses based upon logical conclusions of how the system works and reports, I would hate to guarantee anything. Perhaps a Honda forum where you post “can I turn my ULEV car back into a normal car” get ready for the “greens” to flame you though.