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if you live in a state that don’t have emission testing can you remove catalytic converter.

No, it is illegal under federal law to remove a catalytic converter


Nope. It’s a federal offense.
You’ll also have a hard time selling it unless you put it back on. And if you tried to sell that vehicle to me, I’d report you.

  1. It’s illegal to remove a catalytic converter.

2.It’s physically possible, but not recommended on modern cars (OBD-II compliant) as you’ll end up with driveability problems as the rear O2’s sensors won’t get the kind of reading they are expecting and trying in vain to correct the problem by getting the ECU to compensate the air/fuel mixture to get the post-cat readings within spec, but it’ll never get there because theirs no cat. Now you can get around this with custom ECU tuning. But it’s generally easier just to leave the cat(s) in.

In my younger days, I drove a Bronco with no cats or mufflers for over 200k miles. But it was 1995 model and only had 02 sensors before the cat. The ECU didn’t care about whatever happened downstream of those sensors.

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They actually do sell O2 simulators, that sends false signals to the ECU.

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I would say “Yes,” provided that you don’t intend to resell the vehicle, especially to @MikeInNH, or fear being busted by (Big Brother) the Feds (How, I don’t know…?), ha, ha. In many decades I’ve never been checked by anybody. I live in 2 states with no testing.

However, since you haven’t given the make, model, or model-year of the vehicle, please know that you could run into to complications with sensors reporting erroneous information to the PCM. Triggering running problems or a “Check Engine Light” could prove to be problematic.


I’ve never removed one, but bought several vehicles that already had the cat converter removed. 3 Chevy trucks (1993-1995). They ran fine and were OBD 1, so understandable. Also a 1999 Tacoma (OBD 2), which ran great also. I think in the early OBD 2 vehicles, the post cat 02 sensor must have just been a catalyst monitor with little input on fuel trims. Maybe? Only way I can explain the Tacoma running fine, albeit with the check engine light illuminated.

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I have a 1997 Nissan pickup

That’s all a post cat sensor can do, tell if the cat is functioning. If it is working correctly, there’s no information left to use in setting fuel ratio trims…

Oh yeah I forgot about O2 eliminators. Good catch.

Can you remove the catalytic converter? Sure, and you can probably get away with it, until you don’t.

What I mean by that is that there are several things I could do but don’t, like use untaxed dyed farm fuel in an over-the-road vehicle, or drink alcohol before driving, or drive with an illegal substance in the car, or remove and replace my car’s catalytic converter with a header, that people get away with most of the time, but what happens when I someday encounter an unexpected circumstance? What happens when I’m involved in a collision or a 20-car pileup in winter driving conditions? What happens when a law enforcement officer sees dyed fuel leaking from my vehicle, or notices the missing catalytic converter?

If the unexpected happens to you, will it have been worth it in terms of what you gained by cheating versus what you put at risk? Would the rewards you received by removing your catalytic converter have been worth the risk? I don’t think it is worth the risk, but that’s just me.

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Yeah I agree with @Whitey It’s a federal law and there really is no reason to pull the cat out. Replacements are fairly cheap. At least mine was a little over $100. Just makes no sense and if a guy puts the car up on a lift and sees it, who knows . . .

Not according to point number 2 in Fodaddy’s post above. I’m not certain, myself.

I always assumed the post cat sensor was just a cat monitor / check engine light trigger. But…a guy at work has a Honda Pilot. The cat was bad, replaced it with a Magnaflow and the car wouldn’t run right and engine light stayed on. Replaced the aftermarket cat with the factory unit, all was well. The guy’s not dumb enough to have put an aftermarket cat totally out of spec for the vehicle. He has an older Chevy show truck with a crate 502 that he did all the work on himself. So I could only conclude the post cat 02 may have input on fuel trims on some vehicles.

If the cats are working right, there won’t be anything left to compensate, they will consume the excess. If they are overwhelmed (or non-existent in the OP), then the computer will try to compensate to minimize exhaust emissions and if goes on long enough, set a code. But normally, they shouldn’t have any input on trims if the cats are doing their job. At least that’s my understanding and certainly willing to hear otherwise…

How does the computer try to compensate to minimize emissions other than by adding or subtracting fuel? Maybe I used the term “fuel trims” incorrectly.

The point is, it’s not a normal condition. It would be done only if there is something majorly wrong and a last ditch effort to reduce emissions. The front sensors are all that is needed to develop fuel trims. If they are working, done deal. Now, if the after cat sensors start detecting residual O2, something is wrong. The cats are bad, missing or the engine is way out of whack. Time for desperate measures…

The computer can adjust the air/fuel mixture. It can control the throttle plate position, the fuel injectors, spark timing, and in a newer vehicle, valve timing.

EDIT: The computer can also control the engine’s temperature to minimize emissions.

In 1976 I lived in a jurisdiction that did not have emission regulations at that time. I removed the cat from a 1976 Ford Granada V8 to improve driveability and ease of starting. I kept the cat in case we moved somewhere else that had regulation enforcement.

The mid to late 70s Fords have very primitive emission controls that hampered fuel mileage as well. We’ve come a long way.

Cats in the 70’s and into the 80’s were pretty restrictive. The current honeycomb cats flow very well and do not restrict the exhaust flow much at all. Actually, they act as a fairly decent muffler allowing you to replace the factory muffler with a less restrictive one for the same overall backpressure AND clean air.

Cake and eat it, too!

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I am surprised no one here has asked the obvious question: “WHY do you want to remove the catalytic converter?”

If the answer is “to increase performance” or something like that, don’t bother. Removing a properly functioning cat won’t improve performance, and may actually hurt performance depending on how the computer reacts to seeing it gone.

If the answer is that the cat is plugged up, and causing a drivability problem then you can certainly remove it, or better yet take it off, ream it out, and put it back on. It may not be legal to do this, but if it’s making your car stall out or run poorly, who cares? If you ream it out, and put the empty shell back on, that would also be undetectable by any law enforcement officer or mechanic who might work on the car in the future.