Symptom guide
Rotten Egg Smell From Exhaust
Why sulfur or rotten egg smell may come from the exhaust and what it can indicate.
Quick answer
Rotten egg smell can point to catalytic converter overload, rich running, misfires, fuel quality issues, or exhaust treatment problems.
Most likely causes
- Rich fuel mixture
- Misfire damaging catalyst
- Catalytic converter overheating
- Fuel quality sulfur content
- Oxygen sensor data problem
Basic driver checks
- Check for misfire or fuel trim codes.
- Notice power loss.
- Look for a flashing check engine light.
- Track whether it started after refueling.
DIY diagnostic path
- Do not ignore a flashing light.
- Avoid parking over dry grass if exhaust is very hot.
- Do not replace the converter before fixing misfires or rich conditions.
- Record fuel source and codes.
Common mistakes
- Replacing the catalytic converter without fixing the cause
- Ignoring misfires
- Assuming all sulfur smell is fuel quality
What to tell the mechanic
Ask the shop to diagnose rich running, misfires, and oxygen sensor data before condemning the converter.