An unusual or new smell coming from your car is usually a sign that something is amiss, but it can be even more of an issue if the smell in question is that of rotten eggs. Learn why this happens and how to solve the smelly problem. 

What Can Cause A Rotten Egg Smell In Your Car?

The smell of rotten eggs can be caused by a few different things in your car:

• A blocked or restricted catalytic converter
• A damaged or bad battery
• Mould or fungus inside your air vent system

Can A Broken Catalytic Converter Cause a Rotten Egg Smell?

Yes, one of the most common sources for a smell akin to rotten eggs, is the catalytic converter. If this is the case, it will usually start to smell when the car is up to temperature - around 10-15 minutes into a journey.

The cause of this is not actually the fault of the catalytic converter, but more so the fueling system. If your car’s injectors are adding too much fuel into the cylinders, this unburnt fuel gets expelled out of the engine and is caught in the catalytic converter mesh.

One of the jobs of a catalytic converter is to turn the small amount of Hydrogen Sulfide produced by the engine into odourless Sulphur Dioxide, when excessive amounts of unburnt fuel is reaching the cat, the smell of rotten eggs; Sulphur, can be present inside and out.

The root cause of the issue can be a few things, including malfunctioning injectors, an erroneous sensor, or a broken air flow meter.

Rotten Egg Smell From a Car Battery

If the smell seems to come from near the car battery, and doesn't seem to get worse when you drive, then it likely caused  by a damaged or worn out car battery.

Thanks to the fluid inside, when a car battery is overcharged it can produce Hydrogen Sulfide - yep the same stuff we talked about above! 

A correctly operating alternator and battery setup will not overcharge the battery, but a damaged or worn-out battery can cause issues like this. 

Not only is this gas stinky, it is also dangerous for our health, this is one reason car manufacturers don’t like to mount the battery in the passenger compartment. 

In most cases a new battery, especially if yours is old or looking damaged, will solve the issue.

Can Your Air Vents Go Mouldy and Smell?

Behind the vents on your dash, there are many tubes and ducts that help direct the right temperature air to where you want it. 

If you don’t use this system regularly, condensation and moisture can cause mould to form. 

It might smell all the time, but will be most noticeable when you do eventually use the air conditioning or heater, when any mould or fungus will cause a smell to enter the cabin.

Is Your Car Smelling of Rotten Eggs Dangerous?

Regardless of where the smell is coming from, you should not ignore a rotten egg smell from your car. The gas that is usually the cause, Hydrogen Sulphide, can be very harmful to our health.

Short-term exposure to Hydrogen Sulphide can cause nausea, sickness and throat irritation, prolonged exposure can result in long-term health complications. 

If the smell is coming from mould in your car's vents, then this can be very damaging to your respiratory health, and you stop driving the vehicle immediately.

Should I Take My Car To a Mechanic if It Smells Like Rotten Eggs?

Whether the cause is your catalytic converter, battery or hidden mould, the consequences of not getting the rotten egg smell checked out could be severe. I’d recommend taking your car to a mechanic as soon as you pinpoint the smell to your car. 

In some cases the smell may come and go, it could depend on something as simple as the speed you're driving or even the weather, so try to pay close attention as soon as you smell anything eggy!

How to Prevent Rotten Egg Smell From Coming Back

This will depend on the cause of the problem, but with most of the causes discussed above, there isn’t much you can do once the problem has started, short of fixing the offending component permanently. 

That said, paying attention to your car's service and maintenance schedule can help, not only in the fact your car will run better, but with regular checks from a mechanic, small problems are sure to be found sooner.

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