3 Reasons Your Car Smells like Rotten Eggs

No one likes the lingering presence of an unpleasant or particularly potent smell. When driving, smelling a strong scent like that of sulfur — or “rotten eggs” — is often an indicator of a serious issue.

The smell comes from the small amount hydrogen sulfide, or sulfur, within the fuel. Hydrogen sulfide is usually converted into odorless sulfur dioxide. However, when something breaks within the vehicle’s fuel or exhaust system, it can inhibit this process and create the smell.

The byproducts and deposits causing the smell are left over from the incomplete combustion of gasoline being burned and can be traced to multiple system failures. Should the smell only occur briefly after using the engine at high revs, there is no serious issue to be concerned about. A lingering sulfur smell, however, needs to be investigated. Listed below are 3 reasons your car smells like sulfur.

1. Broken Catalytic Converter

The most likely culprit for a rotten egg smell, the catalytic converter is part of the vehicle’s emissions system. When gasoline reaches the catalytic converter, the converter transforms the trace amounts of hydrogen sulfide into the odorless sulfur dioxide. It is designed to reduce harmful emissions by “converting” exhaust gases, like hydrogen sulfide, into harmless gases. A broken or jammed catalytic converter cannot properly process the sulfur gases and will cause your car to smell like rotten eggs.

Should your catalytic converter be the cause of the smell, you need a new catalytic converter. If your converter is inspected and shows no signs of physical damage, another vehicle component has caused it to fail and needs repair.

2. Failing Fuel Pressure Sensor or Worn Out Fuel Filter

The fuel pressure sensor regulates the use of fuel in a vehicle. Should a fuel pressure regulator fail, it ends up clogging the catalytic converter with too much oil. Too much oil prevents the converter from processing all exhaust byproducts, which then exit the vehicle through the tailpipe and produce the rotten egg odor. An excessive amount of byproducts can also build up within the catalytic converter and cause it to overheat, also contributing to the smell.

In this case, a fuel pressure regulator problem can be fixed by replacing the regulator or fuel filter. A worn out fuel filter leads to the same problems caused by a bad fuel pressure sensor — an influx of sulfur deposits burned up in the catalytic converter.

3. Old Transmission Fluid

If you’ve missed one-too-many transmission flushes, the fluid may begin to leak into other systems and unleash a rotten egg smell. Typically only an occurrence in manual cars, changing transmission fluid as suggested by your car’s manufacturer can often solve the problem. Any leaks that appeared will need addressing as well.

Removing the Rotten Egg Smell

The best way to remove the smell of rotten eggs from your car is to replace the faulty part causing the smell. This could be a catalytic converter, fuel pressure regulator, fuel filter, or even old transmission fluid. Once the appropriate part gets replaced, the smell should disappear.

It’s important to take notice of all off or bad smells surrounding your vehicle. In addition to sulfuric odors, smoking or burning smells can indicate serious issues like an overheating engine, a fluid leak, or worn-out brake pads. Always seek the advice of an expert mechanic when it comes to diagnosing and repairing vehicle components.


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