This tool provides general guidance — not professional mechanical advice. Always have a qualified mechanic inspect your vehicle before making any repair decisions.
#1 Most Likely
Rotten egg or sulfur smell
Typical Cost
$200 – $2,500
Oxygen sensor replacement typically costs $434–$537 per industry repair data (2024). Catalytic converter replacement typically costs $900–$2,500. Urgency reflects worst-case cause (full catalytic converter failure and underlying engine issues). Prices vary by vehicle make and region.
Wide range because the exact repair depends on what's causing the symptom.
- Failing or clogged catalytic converter
- Engine running too rich, overloading the catalytic converter
- Faulty oxygen sensor causing incorrect fuel mixture
- Worn fuel pressure regulator dumping excess fuel
A rotten egg or sulfur smell from the exhaust may indicate a failing catalytic converter that is no longer processing hydrogen sulfide into sulfur dioxide. It can also indicate a fuel system running rich (too much fuel) that is overloading the converter. In the worst case, a completely failed catalytic converter increases emissions, reduces power, and may be an indicator of broader engine problems.
What a mechanic will check
A mechanic will likely scan for fuel system fault codes, test oxygen sensor output upstream and downstream of the catalytic converter, and inspect the converter for damage or meltdown. Fuel pressure and injector operation may also be checked to rule out a rich-running condition.
What to say to your mechanic
“My car has a strong rotten egg or sulfur smell, especially from the exhaust. Can you scan for fault codes and inspect my catalytic converter and oxygen sensors to tell me what may be causing it? I want to understand what component may be at fault before we talk about repairs.”
Script based on industry repair procedures
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