Is it unhealthy to drive with bad catalytic converter?

As in are there any health hazards to driving with a bad catalytic converter if I can sometimes smell the fumes from inside? I can defientely small hard gas smell/fumes once outside the vehicle and my mechanic told me it was a bad cat. It is quite sporadic when I smell it from inside and so not all the time, but now always outside… I am going to change it already in the next few weeks about a month or two of having the rotten egg smell…

Also my mechanic didn’t mention changing anything inside my car (floorwell part?) once replacing the cat, and only to me to buy a replacement one. Does this sound adequate or would other work need to be done it they aren’t telling me about that should be addressed elsewhere?

Why did the converter fail? Running rich? Engine burning oil? Just age/miles? If there is an underlying condition, address that as well or first. It may also be suggested to change oxygen sensors at the same time. This is UNDER most cars so access to the interior shouldn’t be required.

It isn’t ideal to drive this way but shouldn’t kill you or the car. I assume there is a check engine light. If solid, fine. If FLASHING you risk additional damage by driving this. A flashing engine light should be addressed IMMEDIATELY.

As with any car, don’t let it run in an enclosed space. Try to keep moving and turn off the engine if parked for any length of time. You should be fine. The fumes may just be nasty but you might have an exhaust leak as well. That is simple and low-cost to fix compared to anything else needed.


Does my car have oxygen sensors? I have a Nissan Sentra 07 2.0L. Why didn’t my mechanics say anything about this? There is no flashing check engine light on the car right now… And how would I know if I have an exhaust leak and how would I fix that… again no mention of anything by mechanics or why… I feel like they don’t know in all honesty but I could be wrong…

I’m honestly at the point of trying to work on it myself since I would just have to just buy the jack stands and a few other tools but don’t know what real trouble I would come across if anything serious? Do you think it worth a shot? BTW is something like putting antisieze on the catalytic converter bolts necessary? I’m using the direct fit kind of converter. And what about the smell form inside? What is that about again?

Does that indicate you previously had a flashing CEL?
Codes are likely still present, have them read.

Back to your exhaust system. In my opinion, you should go to a dedicated, non-chain exhaust (muffler) shop for a complete exhaust system examination. Likely you need more than just a catalytic converter.
As to O2 sensors, yes you vehicle has them.

Floor wells only need replacing if rusted through, if that is the case, the entire car needs to be evaluated for rust.

I suggest taking this to a shop as mentioned. They will fully understand what is going on.

Yes, I like to use copper (high temp) anti-seize compound on exhaust bolts as it makes future repairs a lot easier.

If you mean the rotten egg smell it is fairly common and just means the cat couldn’t handle everything. Might be an issue with a tired o2 but wouldn’t be concerned if it is occasional. Your. HVAC system draws in air from outside.

If you’re concerned about fumes, put a carbon monoxide detector in your car while you sort this out.


Good ideas above. If you smell exhaust odors when driving at 20 mph or faster, windows closed, that’s definitely the sign of a problem, so good idea to mention that to shop. There may be a path that has developed from the exhaust into the passenger compartment. First step is to make sure all of the exhaust gasses are going out the end of the tailpipe, so there’s no leaks in the exhaust system.

BTW, a leak in the exhaust system could easily confuse the O2 sensors and cause an overly-rich mixture, and resultant damage to cat. Modern O2 sensor controlled engines must be air-tight all the way from engine intake air filter to end of tail pipe. Suggest to not install a replacement cat until the exhaust system is verified leak free.

I once did a entire exhaust on a car . Key word ( once ) never again . A muffler shop can do this for a resonable price and you won’t have dirt and rust falling in your face.


It’s not so bad if you replace the whole thing and have clearance. Just cut the old one up and there are bolts on the manifold. So just like tinker toys. But yeah best to avoid it.

I have only smelled that smell when parked and it’s only been on occasion and never when driving. I have an appt this morning to get my converter changed. Should i cancel it? The mechanic said the cat was oxidized and replacing it would get rid of the smell inside the cabin too. Could this be true? Should i still go to muffler shop?

Is your check engine light on? How many miles? A bad cat should trigger the light.

I have 99,500 miles on it and no check engine light. Never saw one come on either

Then I doubt your cat is bad. How many different tanks of gas have resulted in this odor? Maybe try a different brand?

Can’t say but it’s been over the course of 1 or 2 minths worth or maybe longer so what 20 or 30? Hard to say. I’m going to meineke this morning hoping they can look at itand get a second opinion.

I used to mix mostly between heb brand gas and valeros. I think heb’s is the problem. I think switching only to valeros in a few weeks time made it ease up but not sure since they are supposed to be top tier, but still get that hard fuel smell from outside the car nowdays, not the rotten egg smell per se anymore, but can’t be 100%…

One of the last places for competent vehicle work.


Would it be better I just pay for an inspection at a more reliable place? Do you know any good places? I am in San Antonio, Texas.

Here’s the results of a google maps search, I’d check out shops with more than 100 reviews and a rating of 4.5 or better. Definitely not Meineke.
muffler shop - Google Maps

If it has a Catalytic converter, then it has oxygen sensors.

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I don’t think we have a regular member from San Antonio but as big as it is they might name one no where near you . What is wrong with using or talking to the original mechanic ?