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Confused On What Catalytic Converters to buy

2005 Crown Victoria Bas

So Recently THESE 2CODES popped up on my car

P0420 - P0430
Catalyst System Efficiency Below Threshold (Bank 1 & 2)

I took it to the Mechanic They said Its The Catalytic converters…I Looked online for them I found them but Super Confused on Which One to Get…Idk If I Need to Get The Right,Left, Rear or Front one.they are so many

Looking at rockauto, you have a left and a right assembly. Here’s the list of possible causes. I’m surprised a bad O2 sensor isn’t on the list:
•Three way catalyst converter
•Exhaust tube leaks
•Intake air leaks
•Fuel injectors may be faulty
•Fuel injector leaks
•Spark plugs may be faulty
•Improper ignition timing
•Engine Control Module (ECM)

So why are you looking online for cats rather than the mechanic? Are you planning on buying the cats and having your mechanic put them on?

I don’t recommend that. IF he will install parts you bring him (and some shops won’t), he won’t warranty the parts at all. If he orders the parts, he will get the right parts and warranty the work AND the parts.

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Concur, this job best left to a good shop. Not a diy’er kind of job, at least for most diy’ers. For one thing, the shop will know which cats are legal to install in your area. Not every cat that fits can be used in some places, and having the wrong cat can result in a big fine and/or inability to renew your registration. As posted above, it’s important that the shop who does this has a lot of experience in cat codes, and it is a pretty frequent thing that that code combo doesn’t mean the cat is the problem, often something else. A good shop can confirm the cat is the problem, and whether all the cats need replacing, or just one of them. It’s sort of unusual to see a major cat failure where they all fail in a 12 year old vehicle. The cat in my Corolla is 25 years old and still working. But anything’s possible I guess.

I think this is the same vehicle the OP has 2 other posts about and it has 340000 miles on it and is not worth the price of new catalytic convertors in my opinion. Even if the other problems have been solved.


Your Corolla is OBDI.

OBDI doesn’t monitor catalyst efficiency.

So how do you know whether or not the catalytic converter is working properly?


B/c it passes emissions testing.

Have they done any additional testing to specifically blame the code an a bad cat? There are other reasons you can get a P0420+430 code. Look at “texases” list above.

I’m gonna go to 2more mechanics 1st to get more opinions .because if its any one of those problems I dont wanna Waste my Money on The Cats when its not even the problem

It is probably not as effective as it should be. If your car was operating as it should it would pass the emissions test on the first attempt and you wouldn’t be operating at 99% of the states limits. That is about 20 times the factory specs.

I’m gonna take it to other mechanics so they can see to…because I Passed Emissions like A Month ago With a 100% I’m sure if it was the Cats It would’ve been a problem to pass emissions

I tend to agree with Nevada about George’s cat

Even though the discussion was a few years ago, I seem to remember George’s car BARELY passed the tailpipe test with hc in the high 50s. Sure it passed, but it also makes me think the cat is in marginal shape

And George’s car doesn’t have a rear oxygen sensor, so the catalytic converter efficiency isn’t being monitored. He’ll never get a cat code

This is what I said above about the Corolla’s 25 year old cat:

Didn’t say it was working like new, just “still working”. The engine continues to pass emissions testing in probably the strictest state for emissions levels in the USA, California. Not just idle emissions. Treadmill emissions. And not just HC emissions levels, NOX and CO levels pass too. And they all pass at both treadmill speeds. That’s the only evidence I can cite the Corolla’s cat is working. But it is pretty good and objective evidence the cat is still doing its job imo.

The HC numbers aren’t quite as high as the 50’s from what I recall, 28 I think is what the last HC test was. 30 and under pass. I don’t know what the current type of emissions test would have resulted when the car was new, b/c CA emissions testing didn’t use the treadmill method then, only idle testing. Next spring the Corolla is due for another treadmill re-test. The drama continues … lol

20 to 30 PPM HC is reasonable, the limit is 130 PPM, your car failed with 140 PPM HC. I have tested vehicles with the catalytic converters removed and found the results double that of the typical results but still within the limits.

Now I think about it, you are correct Nevada, the limit is 130, and the Corolla tested and passed at 128 on the final test.

You are correct. You wouldn’t have passed your emissions a month ago if there was a Cat problem. I would think you would have to do some extreme damage to a Cat to kill it after a month…

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