If your vehicle is showing rotten egg or sulfur smell from the exhaust, here are the most likely causes and the parts you'll need to fix each one.
A failing oxygen sensor can trick the engine computer into injecting too much fuel. The excess unburned fuel overwhelms the catalytic converter, causing it to emit a sulfur or rotten egg smell as it struggles to process the exhaust.
Worn spark plugs or bad ignition coils prevent fuel from burning completely in the engine. This raw fuel dumps directly into the exhaust, creating the smell and rapidly damaging the catalytic converter. This can sometimes occur after a recent tune-up if spark plugs are gapped incorrectly or a coil wire is left loose.
The catalytic converter's internal materials have degraded, melted, or become clogged over time. It can no longer properly filter exhaust gases or neutralize the naturally occurring sulfur in the fuel.
A dirty or failing MAF sensor miscalculates the amount of air entering the engine, leading to a rich fuel mixture that produces excessive hydrogen sulfide in the exhaust. This can happen if the sensor is accidentally damaged or left unplugged during an engine air filter replacement.
A mechanical failure in the fuel system can force excessive fuel into the combustion chamber. This severe rich condition creates a strong sulfur smell that the catalytic converter cannot process.