2009 Elantra question - exhaust smell
 

Hi folks, tried searching on this which lead me here, apologies if this has been covered. I have a 2009 Elantra which is in great shape, less than 100,000km on it, like any older vehicle repairs come up, I have to take it in soon to have the brakes done, but have been noticing an exhaust smell in the cabin recently. I had a similar problem in the summer, the O2 sensor was damaged and I had that and the exhaust line repaired, which worked great until recently. When I turn the car on, there's an exhaust smell in the cabin, but it doesn't last very long, goes away after about 5-10 minutes, and I'm noticing it more now in the colder weather, where I have the heat and fan cranked while I'm cleaning the windows. For context, I live in Eastern Canada, Newfoundland specifically and we are in our winter months, on average the temps are around the freezing mark (0 celcius, 32 farenheit), this morning was one of the colder ones we've had lately (-10 celcius, 14 farenheit) and the smell seemed strong, but again went away after a while, I'd say 5 minutes, the windows were frozen so I couldn't "air it out" while I was clearing snow and scraping, I could smell the exhaust smell coming from the front end as well. Before I had the 02 sensor fixed, the gas mileage went from great to terrible, which the garage told me was the car going into "safe mode" and burning way more fuel, this hasn't been happening recently, the gas mileage has been good.

Long story short, wondering if this sounds like something somewhat normal, meaning the smell happening in cold weather, an easy fix like a leak somewhere, or something more serious, which will be an expensive repair. I live in a city with basically zero public transit, need my vehicle to get to and from work, and don't have a lot of cash laying around. To me the car seems to work great other than the above mentioned issue. I will mention this to the garage when I drop it off the get the brakes fixed, but hoping that it won't be a huge expense. I'm quite mechanically "uninclined" so to speak, so hopefully this makes sense, would like to go to the garage with at least an idea of what I'm looking at so I can budget accordingly, any help appreciated!

edit - something I forgot to mention, I primarily do short trips with this car, my commute to work is literally three traffic lights and I can be there in 10 minutes, it's around 10km, not city block lights, arterial roads, frustrating that I can't take public transit but that's for another forum. I rarely take it on the highway, maybe 10 times a year at the most, and even then it's only an hour drive to and from, I have friends who live in another town and sometimes take a road trip. Only mentioning this in case the short trips might help nail down the issue

There is a good possibility that when replacing the oxygen sensor they moved/disturbed a connection in the exhaust system coming from the engine to the converter and remainder of the exhaust piping. Many times the leak will diminish or seal as the exhaust system gets hot and expands. I would suggest that you have the shop that last worked on your vehicle check for an exhaust system leak. They would need to allow the system to cool down to do a thorough job and start it when cold to get the same symptoms you are getting.

Thank you for the reply, I will be taking it to the same garage, it's near my work and they're a reputable spot, if they knocked something loose during the last repair I'm quite confident they'll fix it no problem.