Replace catalytic converter or not?

I was told that my 1997 kia Sephia needed a new catalytic converter by a very reliable shop. My car had been stalling out and running very rough. They did replace the distributor cap which seems to have helped the overall performance and that same day i had a smog check and passed with flying colors! Why would I still need to replace my converter if I passed smog. My car has only 36k on it.

please someone advise …thanks!


I’m a little perplexed, also

Please post your smog results . . . can you scan it in?

Is the car low on power?

Is it still running rough?

If the cat was in horrendous shape, you would have had a P0420 catalyst efficienty fault code, which would have illuminated the check engine light, which would have meant a smog test failure.

Cat converters can fail in one of three ways.

  1. they can leak.
    Leaking can trip a CEL depending on where and how bit it is, but will not affect vehicle performance.

  2. their efficiency in dealing with the NOx can deteriorate
    Efficiency drop will trip the CEL, but not affect performance.

  3. they can become plugged up.
    Plugging will affect vehicle performance but may not trip a CEL. Plugging will cause poor power and rough operation.

You need to ask the shop why they feel you need a new converter. Without knowing their reason, it’s hard to second guess them.

Thank you both for the posts! the car is not running nearly as bad before. I think the replacement of distributor cap helped. The car seems fine on power, some hesitation first thing in a.m. If it is “plugged up”, do cat “cleaners” work? replacement of this cat will cost about $4500…ouch! With such low mileage and car in excellent overall shape, I hate to purchase something else.

There had to have been a “check engine light” involved here. If so, then find and post the exact codes that came from the computer - they look like “P0123”

If you have no check engine light now and the car is running well, then you don’t need to do anything.

Have you thought about getting a second opinion? I just had my cat con replaced on my 2002 Subaru Outback, the check engine light was on. It cost me $680.


cat cleaner sounds like snake oil

Can you please post those smog results, as I asked you to?

If the vehicle passed the smog test it means the Check Engine light wasn’t on.

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



But the cat might be in marginal condition

That is the reason I wanted to see the smog test results

All I can do is offer some experience here. My sister had an old land rover and a cat went bad. Of course the dealer wanted some ungodly amount to fix it. Their “fix” was to replace the entire mid pipe (a whole new cat system). Thousands of $.

I took her to a local non chain muffler shop and had them hack out the bad cat and weld in a new one. Cost a little over $100.

My mustang had one go bad in the high performance mid pipe I put on. Sounded like a rattly coke can. No check engine light. I bought a new one and put it in myself (the pipe was modular and used clamps). Problem solved.

There seems to be several people on here that are being taken by their mechanics big time for cat problems.

Granted if one side fails the other certainly can go bad down the road and or even the replacement itself if its a cheap one. But for gods sake dont spend $4500. Thats silly

I don’t think you want to spend $4500 on a 97 Kia, period. Second opinion for sure, then tape on the CEL and look for a replacement vehicle.

About $200 at Rockauto for a 1.8L, except for California or NY. If a 1.6, there may be an availability problem.


It’s not so simple in California

The cat needs to be certified

Those $100 generic one size fits all are no longer permitted as replacements

Theres one for $52.00. What the hell are your mechanics smoking!!?

Ahhhh!!! Sorry didnt see this was a california situation. Of course it would be

This ones california legal and about $430. Still better than $4,500!

Maybe you should get a few more opinions. A car with only 36k miles should not have 4500 dollars worth of converter issues considering that you passed smog and the car is running reasonably well.
One has to wonder about the diagnosis and also whether a distributor cap was the cause of any problems. Unless the cap was cracked or carbon tracked it shouldn’t be an issue.

I will scan smog results tomorrow for those interested. Overall, sounds like I will return to the “shop” and discuss all of your comments and go from there. Check engine light has not come on once dist. cap was replaced. Could “loose belts” cause my problem? I was told they need replacement on my next visit. Thanks all…will check in tomorrow. REALLY appreciate your expertise!

I dont think belts would cause the problem unless they were really bad. If theyre cracked or worn then by all means go ahead and replace them. Thats cheap.

Id certainly go to a different shop.

If the car runs fine and youve passed inspection then forget about it and drive it. Just make sure the belts are in good shape - otherwise they could break and leave you stranded. Not expensive.

As an alternative add a dose of sea fome and find a state where you can run it at 100 mph for an hour or so, nothing to loose as far as I see.

For those requesting smog test results, here they are. Photo quality is best I could get. hope this helps with diagnosis.