2002 Buick Regal LS with 65,000 miles second catalytic bad converter

2002 Buick Regal LS with 65,000 miles is on second bad catalytic converter. It was my mom’s car she bought it with 32,000 miles, it was willed to me and have had it for 6 monthes. I just got a P420 code. The first mechanic charged me for a rear o2 sensor. Two weeks later a p420 code back on. 2nd mechanic changed from the resenator to the muffler. P420 came back on a week later. Opened the hood and the air filter box cracked open on bottom. Closed it and cleared code but now told have to buy a 3rd catalic converter. How do I know if I really doo need a $1000 new cc. Why would these go bad? I have to contact my mom’s mechanic but I assumed the first one should have been under the federal warrenty and it was replaced with aftermarket part that wasn’t California/ New york leagle? Code has not come back on (yet) but haven’t driven much.New pipes and parts make creaking sounds constantly unless off and cold. Should I run a bottle of cataclean through the system? Never owned a car before last year, what should I do next. Father bought me a 2005 Grand Caravan with 230,000 miles (now has 263,000 miles) last year which broke down a day after the buick.Ugh and help.

A cat converter fails early mostly for two reasons:
There’s another problem that killed it, or it was a cheap aftermarket unit with poor durability.
Do you know when the first converter was replaced? Before or after the purchase at 32k miles?

This car did a stretch where it wasn’t driven much, to average 5000mi per year.
Cars like this often don’t get proper maintenance. Many services should be done based on time as well as mileage.
Does the engine burn oil? How much between oil changes?
How often has the oil changed, in terms of miles and time?
How long since spark plugs (& wires if it’s got them) been changed?

In addition to circuitsmith’s excellent post, 65,000 miles on a 13 year old car suggests a life of very short local trips. Engines are intentionally run rich when cold, and that produces more of the exhaust components that coat the car converter’s internals. That can cause it to become inefficient in far fewer miles than a converter in a car that’s regularly highway driven.

If it were mine, I’d replace the converter, give it a good thorough tuneup, get it all checked out, and say a prayer of thanks to my mom.

If the code does not come back, keep driving.

My kid had a few modded grand priixs. He put new systems on 2 different cars, never had any cat issue/codes. It’s easy to find a plug in cat simulator. $50 online. It will get rid of code. But knowingly driving with a failed emission car is not exactly legal. Or maybe it is?

I might point out that P0420 does not necessarily mean the catalytic converter is bad

Here are some other things that could be a factor in that dtc

oxygen sensor(s)
exhaust leaks

I think it’s time for better diagnosis, before throwing another cat at the problem

I have not heard enough “evidence” at this point to assume the cat is toast

Remember, a dtc is not the answer, only a starting point

There are tests which could evaluate the cat’s condition. Throwing parts at the vehicle is not testing

I’ll go a little off-topic now . . . dirt cheap $100 cats, for example, are not expected to last very long. Their purpose is to get the car past the upcoming smog inspection. No more.


For the computer to keep the air fuel mixture correct, the engine has to be air tight from the air filter box to the tailpipe. No leaks. Otherwise the mixture could be off, and that will damage the converter over time. Since your air filter box is cracked, suggest to replace that part, then have your shop check for any other air leaks. It’s especially important there be no leaks in the path from the air filter box to the throttle body, nor from the engine/exhaust manifold gasket to the rear O2 sensors. A vacuum system inspection is usually part of this.

Ok I’m back, sorry so long.

Car not seeming to using much oil, I had the oil changed April or May and was told to change it at 5,000 miles which it’s now due because of long trip. only had to top it off with 1/4 qt from oil change. Brother said plugs and wires ok but I’d like to learn to change them myself (hubby use to do all this stuff himself). I was thinking about cleaning MAF, filter is clean. I only had to properly place the air filter back in and closed the compartment, I put Luke’s fuel injection deep clean and drove 700 miles (back to do mom’s ash ceremony) Got a P440 and gas cap needed tightened. Drove home 700 miles fine didn’t go anywhere for 2 days and then got the p420 again.

It’s true mom did not drive much and short trips. I also don’t go much (hubby has ALZ) but little further distances highway and local but not daily. I picked up her repair records from her last mechanic (only one I knew of) If the Cat was replaced (although it doesn’t look like the pic of an oem cat) it must have been before she got it, I think she got it at 32,000 miles. Is there a way to look up the vin to see if cat was replaced? She serviced it regularly, her state has inspections not smog, my state has smog only.

This week the car started smoking, took it in to the guy who said 420 means to replace Cat only. He told me the rack and pinion power steering line is leaking, that I need to replace the whole R&P because the Power Steering only lines can’t replaced that he has to replace the whole R&P but my mom had the R&P replaced 06/14. I got the car back, jacked it up, yes the R&P bar did rub a hole in the metal PS line. I cut a old washer hot water hose slipped it between the bar and line to slow the leak.Will this rubber burn, is the PS line hot?

While under there I looked at the exhaust line. The guy who replaced the resonator cut off the flange after the cat and new o2 sensor and welded it to the pipe (and put the lowest quality parts on, pipes creek and crack). where the weld is I see a wet looking stain on frame. Can I put quick steel putty on the weld in case there is a pin hole in the weld? Also while under there i saw a 3 or 4 " pipe or cylinder with a rubber cap that is crack open. It’s to the right and underneath of the master brake cylinder. I don’t know what it is. I also turned the car on for 10 or 15 mins to see the drip but the fans didn’t kick on but I don’t know when they should.

My mom’s mechanic said the replace gas cap. I looked at it and the gasket is cracked. Just to give you an Idea of the car stress, the car we had before the inherited Buick is a 05 grand caravan with 265,000miles that suddenly the radio, 12v plug, wipers/pump, windows, horn and ac not working when on but if i turn it to battery the wiper, radio and windows will work. so I can’t drive either cars. UGH

Wow, that was a lot of information

A rotten gas cap seal can certainly cause P0440. Replace the cap, it’s a no-brainer. If it was the cause of the code, it will eventually clear itself

As far as P0420, any exhaust leaks and cracks are certainly a factor . . . since the O2 sensors read oxygen content

A mechanic with an evap/smoke machine could very quickly check to see if your exhaust system is tight, or if it has lots of leaks. Sometimes, you can rack the car, let it idle and CAREFULLY run your hand down the entire length of the exhaust system, checking for leaks. Leaks can sometimes be felt as a puff of air. But the smoke machine is more reliable and safer for you.

I’m kind of skeptical of the power steering rack diagnosis. Meaning last year’s repair was a lousy one, meaning lousy parts or lousy workmanship

“R&B bar” . . . please clarify

I know “R&B” means rack and pinion, but what do you mean with “bar” . . . ?

There are some power steering lines that are considered to be part of the rack, and aren’t available separately, by the way. But there are also some o-rings and gaskets which can be replaced individually. Since I can’t see your leak, I can’t really make a judgement.

Just for your information, there ARE some cheapo aftermarket cats out there, that just aren’t good enough. Meaning they’re so lousy, that the P0420 will return. Aftermarket cats have various numbers on them, and the mechanic should be able . . . if he’s got the patience . . . to determine if it’s the correct application for your car. Sometimes unscrupulous/lazy guys will weld in a “wrong” cat. And the result will be a failed tailpipe test and/or a P0420 code and check engine light on. I’ve seen this happen a few times