If you notice a sulfur or rotten egg smell coming from your car, it’s usually a sign of a problem in the fuel or exhaust system. This smell is often caused by the catalytic converter not processing exhaust gases properly, or by excess sulfur in the fuel. While it may seem minor, ignoring it can lead to costly repairs and harmful emissions.

What does a sulfur or rotten egg smell mean?

The smell occurs when hydrogen sulfide in the fuel doesn’t convert properly into sulfur dioxide in the catalytic converter. This usually indicates a failing catalytic converter, fuel system issue, or engine misfire that is sending unburned fuel into the exhaust.

Common causes of sulfur smell in a car

• Failing catalytic converter
• Faulty fuel pressure regulator sending too much fuel
• Engine misfires causing unburned fuel in exhaust
• Old or poor-quality fuel with high sulfur content
• Blocked or failing oxygen sensor

Why do you need to fix this problem quickly?

A strong sulfur smell is more than unpleasant — it’s a warning sign that the catalytic converter or fuel system is not working properly. Ignoring it can lead to reduced performance, higher emissions, and costly damage to the catalytic converter.

How do you know when to get it checked?

You should book an inspection if:

• You smell rotten eggs inside or outside the vehicle
• The Check Engine Light is illuminated
• You notice poor acceleration or reduced fuel economy
• The smell gets stronger after driving for a while

What happens during an assessment?

A mechanic will:

1. Inspect the catalytic converter and exhaust system
2. Check oxygen sensors and fuel injectors
3. Test for misfires and scan ECU for fault codes
4. Check the fuel pressure regulator and fuel quality
5. Advise on necessary repairs or replacements

How much does it cost to fix?

Costs depend on the fault. Oxygen sensor replacement may cost $250–$500. A new catalytic converter typically costs $1,200–$2,500+. Fuel system repairs can range from $300–$900.

Is it unsafe to drive with a sulfur smell?

Yes. The smell indicates that harmful gases may not be treated correctly by the exhaust system. Driving with this issue risks engine damage, failed emissions tests, and exposure to toxic fumes. It should be inspected promptly.