Why does my car smell like rotten eggs?
Answered by Super Tire & Muffler · Updated June 19, 2026
Short answer
A rotten-egg (sulfur) smell from a car almost always points to the catalytic converter not processing exhaust gases properly, often because the engine is running too rich or the converter is failing. It can also come from an aging battery in some cases. Because it usually ties back to a fuel or emissions problem, it is worth getting diagnosed. We can pinpoint the cause.
What is happening
Fuel contains trace sulfur, and a healthy catalytic converter turns it into odorless gas. When the engine runs rich or the converter is worn, that sulfur escapes as the rotten-egg smell. A bad oxygen sensor, fuel injector, or fuel-pressure problem can be the root cause feeding the converter too much fuel.
Ignoring it can let a fixable fuel issue turn into a failed converter, so it is better to chase it down early.