We got this question via email:
Hi. I’ve got a newer Mazda and, while I love the car, there’s a rotten egg smell that I really can’t stand. I asked the dealership and they told me to try a different gas station. Any other advice you can give?
Chances are, if you have this problem, your gasoline source is to blame. Cheap gasoline (or gasoline from an older gas station with old tanks) can be contaminated with sulfur, and during combustion this sulfur can bond with hydrogen to create a compound called hydrogen sulfide that smells terrible.
However, it’s also possible that your vehicle’s catalytic converter or fuel system isn’t functioning correctly. My advice:
1. First I would take the car on a long highway trip (at least 2 hours of continuous use). That can help “clean out” the catalytic converter, which might just cure the problem…you might have purchased a bad batch of gasoline with a lot of sulfur in it, which in turn contaminated the cat. A long drive will burn off most of the sulfur.
2. Depending on the cost, you can try buying an emissions system test. The emissions testing gear can tell you if the catalytic converter is damaged or not working properly. If it’s broken, Mazda will replace it with a copy of the failed test.
However, the odds of your catalytic converter being damaged or not working properly are very low.
3. Check to make sure you’re using the correct octane/grade of fuel. Your vehicle owner’s manual probably recommends 87 or higher, but you should double-check to be sure.
4. Watch for any sort of check engine codes.
5. Try a few different gas stations (one at a time) and see if the smell gets better or worse. You may have to try a couple of tanks full of gas to know for sure if things are improving (it may take several weeks to figure this out).
6. If none of this works, you can try disconnecting your battery for 30 mins. This will reset all your radio presets, but it will also reset your engine computer. I’d try this last as it could make the problem worse.