Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

New GM Catalytic Converter vs. After Market

We own a 2000 Buick Regal with close to 120,000 miles. It was a highway driven car when we bought it for our kids to drive so the mileage didn’t bother us too much. Recently, it was not accelerating well and at first we thought it was the transmission but our mechanic told us it was a blocked catalytic converter. He told us it HAD to be a new GM converter, couldn’t be used and couldn’t be after market. He told me they had used after market converters in the past and they didn’t fit or they didn’t work well. The new part is $587. On a car with close to 120,000. Is he telling me the truth? Should we spend that much money on a part on a car with that many miles?

Other Buick owners have had no problems with aftermarket catalytic converters. Find another mechanic, get a second opinion, and ask if he will install a part that you supply. Some will, some won’t.

Back in the late 70s you had to buy your converter from the manufacturer. Today there are good aftermarket converters for many high volume cars such as yours, at fraction of the dealer price.

Your mechanic is right about the fit-- usually a OEM convertor will bolt right on, wheras an aftermarket one will often require cutting and welding to get it in. However, as you know, the price difference is quite substantial and, though it’ll cost you a little bit more to have it installed, the cheaper part should more than pay for this. Most regular mechanics simply don’t like having to do welding on the exhaust system and prefer the bolt-on style, but an exhaust shop shouldn’t care either way.

As for how well they work, that’s a little more difficult to tell. Aftermarket convertors generally work very well in most applications, but if you’re in a state that has very stringent emissions testing, there is a chance that the aftermarket one won’t work quite right with your specific application and you may have some troubles with your smog test. Most exhaust shops in these areas will guarantee that their aftermarket convertors will pass, though it will be an enormous hassle proving to them that the convertor is the problem.

A direct fit aftermarket converter for your car is $200. The mechanic is probably worried about fit and quality and wants to avoid hassle, and in my experience he’s probably got a point. However, given the cost difference I’d propose this. Tell him you’d like to purchase a direct fit aftermarket and try it out and see if it works at your own expense. If it fits great. If it doesn’t tell him you’ll pay him for the attempt and get the factory GM conveter instead. Take the gamble, you might save some cash. Go to AutoZone/Advance/Etc get the direct fit and bring it to him.

Thank you SO much for all of your suggestions! They are extremely helpful in helping us make our decision on what do to. I appreciate it very much!

An aftermarket convertor MIGHT trigger a code. I have seen it. In this instance the exhaust passed throught the convertor to fast and told the engine it was not operating at the proper temp. I am not saying it will happen but it might. On an 8 year old car with 120000 I would live with the ses light on if it was a big price difference.

There are aftermarket and ‘aftermarket’ cats.

Aftermarket cats built with the same exhaust section and built specifically for that car that do not alter the original design in any way are okay. Though they may not be as good as an OEM part.

‘Aftermarket’ cats that you have to plumb into the exhaust need a documented statement as to the reasons why it was installed i.e. “If a state or local inspection program has determined the existing converter has been lead-poisoned or damaged or otherwise needs replacement”

You just don’t need the trouble, fit the OEM part and be done with it.


I think what you’re trying to say is that there’s “Direct Fit” and there’s “Universal Fit”. The universals are usually a headache but a direct fit is a direct fit and it should bolt right up most of the time. I’ve done more exhaust work on cars over the past ten years than I care to admit and I’ve had reasonable success with direct fit converters in a non-specialty application. If she had a VW or BMW I’d say forget it, but it’s a Buick. If it’s a poor fit she can always return it to Autozone no harm done.

This is the first time I have ever seen a complaint about an aftermarket cat.

The muffler shop will not complain about the aftermarket parts that they order and install or have on the shelf and install. It’s just a thing with stuff inside. Kind of like an watch with an aftermarket watch battery.

Don’t work for a muffler shop. The work is exhausting.