Exhaust Smell Diagnosis
Fix Soon
A rotten egg or sulfur smell from the exhaust is most often caused by a failing or clogged catalytic converter, or by an engine running too rich. When the engine burns excess fuel, the converter cannot process all the sulfur compounds in the exhaust. Oxygen sensor faults, clogged injectors, and mass airflow sensor issues can all cause the rich condition that produces the smell.
Get this checked soon — it will get worse over time.
Check These First
Before diving into diagnosis, quickly verify these:
- 1Note whether the smell is strongest at the tailpipe, inside the cabin with windows up, or at idle vs. highway speed.
- 2Check whether the check engine light is on — a P0420 or similar code points directly to the catalytic converter.
- 3Note whether performance has changed alongside the smell — sluggishness, hesitation, or reduced fuel economy.
- 4Check whether the smell is more pronounced after a cold start or when the engine is under load.
- 5If the exhaust smell is entering the cabin, check for exhaust leaks ahead of the passenger compartment.
What exactly is it doing?
Pick the description that fits best.