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2012 Nissan Altima Catalytic Converter Smell and Sound

This is a long story, but I’ll try to get right to the gist of things. My mom drives a 2012 Nissan Altima that has over 200K miles on it from daily commuting to work (I ride with her since we work at the same place). About a month and a half ago, we were at a drive-through waiting to place an order for our lunch when the most horrible smell came into the car. It smelled like a mixture of kerosene, propane and natural gas and it was making us both sick. We thought it might be a natural gas line outside of the restaurant so when we got our order told them how bad it smelled. When we got home to eat, my mom parked in our enclosed garage, we got our food and drinks together and horror of horrors, the stench was in the garage. She called a mechanic that she trusts to come over and see what was going on. He came right away and said that her catalytic converters were clogged and he was going to see if he could clean them or if they had to be replaced. We were hoping for cleaning since replacing was going to cost in the $1,000 dollar range. He called back the next day and said he was able to clean them and that was a relief (or so we thought). Now, the trouble is, the car has been smelling almost like a diesel truck ever since and I’m wondering about this so-called cleaning because everywhere I look on the internet seems to suggest that it isn’t possible. The smell was obnoxious for the first month and it was embarrassing to have anyone near the car when it was running because of it. Now, it’s not quite as bad, but it’s still there, lingering in our garage for a number of hours after driving. I also noticed that the car almost sounds like a diesel engine when my mom accelerates, sort of like cars that are ‘souped-up’ with a low, rumbly noise going on in the engine, but that could be something else. I’m just concerned that this odor is a signal of a rip-off job. Need to add that the smell comes from the front only, particularly right around the passenger side tire area and does not smell at all in the back.

Have the vehicle inspected by an automotive technician, not a guy that cleans catalytic converters. Stinky exhaust will go away in less than a minute after shutting off the engine.

The odor that you have may be from a plastic bag that has melted to the exhaust pipe but that would go away after a month. The odor could be from motor oil leaking onto the exhaust pipe.

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