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Catalytic Converter for VW Passat 2003 V6 - Original or OEM?

I got an engine check condition that ended up being a Catalytic Converter problem - both of them, in fact (I looked at the results of the reading - one existing code for the right converter, and a saved code for the left one.) My mechanic said I should replace both at a cost of $1100 each + tax + labor. He recommended against used parts, but I see that I can get new OEM converters for $387 each, with 5 years/50000 miles warranty (Eastern Catalytic). They say installation is easy.

I really want to trust my mechanic, but I can’t understand why he recommends to me a $2500 service. I live in Massachusetts - I don’t think we have a CA emissions rule that should prevent me from using these parts (but please correct me if I’m wrong.)


Go with the mechanic’s recommendation or with the OEM parts?

Anybody knows anything about Eastern Catalytic?

Should the left/right part be identical? RockAuto parts sells different left/right converters (part numbers 40463/40464)

I’ve never done any work on the car myself - is it something I should be able to do or should I first find a mechanic who’ll do the work for me?

Thank you for your help… and please be easy on me, I’m not as savvy as some of the people on this forum!

An after market converter is fine. It will save you money and it must meet the same specifications as the OEM converter. It is covered under federal law. Your mechanic is correct and is trying to save you money.

My mechanic is the one recommending against it…

I’d like to know more about the codes. There is no code that says, “Replace Catalytic Converter.”

If the code said something like “Catalytic converter bank one below threshold,” it does NOT necessarily mean the converter is bad.

People spend lots of money replacing converters that don’t need to be replaced, and then are very unhappy when the CEL comes back on. Often another problem, such as a worn oxygen sensor, is causing the converter to operate outside its normal range.

How much diagnostic testing was done before your mechanic recommended new converters? Did he test any other components, or was reading the codes the extent of it?

The codes where “Catalyst System Efficiency Below Threshold (Bank 1)” and “Catalyst System Efficiency Below Threshold (Bank 2)” - I’m not sure about the exact code numbers, but I’ll have it checked tomorrow again. He didn’t do any other diagnostics, but he reset the check condition and told me to see if it triggers again. A couple of days later the engine check went on again - I’m going to see him tomorrow and probably see the exact same thing. I’ll post the codes then. I’m also going to ask him about OEM parts. From what I’ve read here (and in other discussions) people seem to think it’s a good idea. I certainly like the idea of paying $800 instead of $2500.

Someone needs to test some of the other components of the emissions control system. These codes do not automatically mean you need new catalytic converters.

Cats are expensive. Don’t buy them until you’re absolutely sure they are necessary. These codes do not indicate you need new converters.

I just bought a 2003 Passat with 145K only to have the check engine light go on a week later. Now I am being told both cats are bad. I suspect (but will confirm) that this dx was based on the codes. What should I be asking them to do? Is it OK to get used cats in CA?

When a code for “Catalyst System Efficiency Below Threshhold” shows up, you can pretty much take for granted there’s a problem with the catalytic converter(s). This is determined by the amount oxygen the post catalytic converter O2 sensor detects. If the O2 sensor detects oxygen leaving the catalytic converter, it means the oxygen isn’t being absorbed by the catalytic converter substrate to cause a catalyst reaction. So the catalyst efficiency falls off.

You cannot purchase used catalytic converters from an auto recycler. This is against EPA regulations and fines can be as much as $20,000 for each used catalytic converter sold.

There’s nothing wrong with installing aftermarket catalytic converters. These must meet the same stringent EPA standards as the catalytic converter that orginally came on the vehicle. Besides, auto makers don’t make their own catalytic converters. They purchase them from a supplier. So as far as the mechanic knows, the aftermarket catalytic converter could come from the same company that supplied the catalytic converters when the vehicle was built.


The FIRST thing that needs to be done, before you dump a ton of money on converters, is to have the thing properly diagnosed… as other techs here have stated.

Most vehicles have a pre and post catalyst O2 sensor, the post-catalyst sensor often being referred to as a fuel/air ratio sensor or similar. Assuming all sensors pre-combustion are operating properly and not causing a change in fuel ratio, a malfunctioning O2 sensor can cause the computer to interpret a particular O2 sensor’s output voltage as being a result of low catalyst efficiency, when in fact it is not.

A competent (not to imply your mechanic is incompetent) diagnostic technician will have a scanner with sufficient access to certain computer functions to scope and graph the output voltages of your O2 sensors. Being a German vehicle, this usually means that a good deal of ECM functions are locked out of the “standard” data stream that is mandated by federal law for manufacturers selling in the U.S. to provide as “open” to a technician with OBD-2 reading capability. O2 output voltages should be able to be read by a very modest scan tool, but other engine functions may be locked out if your mechanic has not purchased the proper access software for his scanning machine… and usually the only ones that bother with VW/BMW/MB software are Euro specialty shops.

As far as your question regarding a USED catalytic converter that your mechanic is against-- he couldn’t sell you one even if he could somehow find one. Thanks to the statist boobs running various aspects of our government, some genius decided that to save the planet (go watch George Carlin on that one) we’re gonna force consumers to strap on all sorts of emissions gear to put out less goo into the environment, fine. But, those same boobs then decide to really jam it into the consumer’s back side by coming up with various regulations like the one that bans salvage yards and the like from allowing the sale of catalytic converters. Where I live the local you-pull-it salvage yard cuts all the catalytic converters out of the vehicles along with draining the fluids before putting it in the yard to be picked. It’s OK to sell a used car with its used catalytic converter, but don’t you dare take good parts off a kaput car, such as the catalysts, and sell them separate… Big Brother loves the little guy who is working his butt off to make ends meet and his heavily used car’s catalyst craps out on him. As you can see on or any other parts dealer online, all the direct-fit aftermarket catalysts for your VW say “Not legal for sale on vehicles licensed in California.” The poor serfs living in the state of fruit and nuts not only have to deal with the feds, but their own state as well.

Assuming your catalytic converters ARE in fact used up (hey, after 8 years of driving I’d say they served you pretty well) you can probably do the job yourself, even without a lift. If you don’t have severe corrosion on the exhaust, you can unbolt the catalytic and it’s rather long pipe assembly (50" on your vehicle it looks like), and bolt the new one into it’s place. I would get 4 jack stands and jack the vehicle up on a flat spot, and go to town.

Concerning price: being a former service manager, it sounds like your mechanic quoted you a price for dealer-sourced parts, or he’s just trying to take you for a ride and REALLY club the baby seal. Aftermarket parts are usually available to shops on a commercial level for anywhere from a third to two thirds of what those same aftermarket prices cost Joe Schmoe over the counter. As a result, the markup for those parts generally tends to be anywhere from 50 to 100 percent (sometimes more), depending on what kind of part it is. Dealers however usually don’t cut any slack to commercial garages, so a part that costs 100 bucks at a dealer for Joe S will be offered to a garage for 85 bucks. When I ran a shop the local VW was BRUTAL to us… so as a result I would simply tell some customers that due to the cost and the markup my company was looking for keeping me employed and the bean counters off my arse, it would simply be unethical to sell them that part for such an insane price.

I imagine those same catalytic converters from VW are probably in the $600-800 range, so a markup to $1100 is not unreasonable for a brick-and-mortar establishment that has to pay insane utility bills, worker’s comp insurance, unemployment insurance, and all sorts of other huge overhead in addition to paying their talent a paycheck. Labor shouldn’t be more than 2 hours for this job. Obviously costs are a concern, and I don’t see any advantage to using overpriced ffffolksvaaagen converters. Talk to him about getting the aftermarket ones. That should keep you around $1200 installed.

Thanks so much for the thoughtful replies. One last question. Is it odd that both cats should go out at the same time? Does the computer show when they first went out? I am wondering if the used car dealer who sold me this car had the codes reset prior to the sale.


That is a possibility, but forget just “reading” the codes, you need to have the output of your O2 sensors and some other items graphed so their function can be interpreted.

Usually, yes you’re right, two cats won’t go out at exactly the same time, but within weeks or months (or maybe more) of each other. When EVERYTHING else on the vehicle is functioning properly and a cat starts to go, you get a catalyst efficiency code, but not always (back to that proper diagnostic thing).

Best of luck, let me know what your technician says after doing some graphing and analysis.

Oh yeah… the last time the computer was reset should be available in the OBD2 datastream that should be read by most code-read type scanners.

Hello , I got the same code Catalyst System Efficiency Below Threshold (Bank 1)… I want to start first with changing the sensors . I’m not a mechanic so I’m trying to change it by myself . Can you please tell me if you k ow , which one is bank 1 ? If I’m faced to the engine is it the left or right one ? Which one you recommend to change it first the upper one or the downer . I’m willing to change them both , but at Oreilly or autozone they’re cost is like 170$ each . Do you know a cheaper site I could buy it from ? Thank you in advance . Danix

Helpful hint. You’ll get better responses if you post your problem to its own thread rather than tagging onto this thread.

For another source for the O2 sensors, check w/ They might be a little less expensive there, mail order. They usually have photos so you can compare to what yours looks like.

W/a V6 engine configured w/ two cats there’s probably 4 O2 sensors involved. One before and one after each cat, and one cat per bank. Sorry, don’t know which is bank 1 for VW’s . Usually it would be the same side as spark plug number one tho if that is of any help. On older American iron v8’s, spark plug number one is the one furthest forward, furthest toward the front of the engine. Whether that applies to VW, don’t know. But since you are just guessing anyway, choose a side and replace both sensors on that side maybe. Who cares if it is bank 1 or 2?

I should add for completeness, I doubt the O2 sensors are what are causing your problem. O2 sensors are pretty robust. I think you’d spend your $$ better by finding a good inde shop and getting a proper diagnosis. Once you know what the problem is you can fix it yourself if you like.