Why Does My Car Smell Like Rotten Eggs?

Your car smells like rotten eggs may indicate something serious with the engine. It’s time for car maintenance.

This article discusses what causes your car to smell like rotten eggs, how to deal with it, and what to do to prevent it from reoccurring.

Is Rotten Egg Smell In Car Dangerous?

Some people may think they can drive their car and let it “air out” before the smell goes away. However, you should not drive with a rotten egg smell in your car. It is possible to indicate that your car had terrible problems.

Why Does My Car Smell Like Rotten Eggs?

There are three most common causes of a rotten egg smell inside car. They are a defective or broken catalytic converter (cat), an old transmission fluid leak, and fuel system issues.

Cause 1. A Leak in The Exhaust System

A Leak in The Exhaust System cause rotten egg smell in cars

The exhaust system is designed to filter out pollutants, moisture and other harmful gases. However, if the car has a leak in its exhaust system somewhere close to the engine or around the catalytic converter, hydrogen sulfide may find its way into the passenger compartment.

A catalytic converter handles the minimization of toxic emissions. It does so by changing the hydrogen sulfide produced in your car to non-toxic gases like sulfur dioxide. The failure of the converter to perform this task will lead to the emergence of a rotten egg smell.

What you think is a rotten egg smell is most likely the smell of the element known as sulfur. The fuel used by your car has hydrogen sulfide, which contains this element.

What to do?

Inspect the catalytic converter for faults or signs of physical damage. You will need to purchase a new one if it looks damaged or faulty. The best and safest step to take is to replace the cat. You can use the catalytic converter cleaner to clear out blockages, but it may not be effective at eliminating the smell. Shift the suspicion to other vehicle parts if the cat looks OK.

You can use an OBDII Scanner to inspect the problem.

ANCEL AD310 Classic Enhanced Universal OBD II Scanner


Autel OBD2 Scanner

Autel OBD2 Scanner

How To Fix Catalytic Converter Leak?

Cause 2. Old Transmission Fluid Leak

Old Transmission Fluid Leak cause rotten egg smell in car

Transmission fluid lubricates and cools the internal parts of your car’s transmission. It can be amber or red. The leaking of this fluid would be harmful to the transmission and nearby systems. It must be changed regularly.
Your car may smell rotten eggs when the stale transmission fluid is leaking into other systems in the vehicle. This usually occurs in manual cars. The fluid gets burned as it comes in contact with hot engine components.

What to do?

Wipe off the leaked fluid and swap out the worn-out parts. You would need to buy new transmission fluid as well. Check the nearby systems to ensure that they haven’t been affected by the leak. Clean and repair them if necessary.

How to Diagnose Transmission Leaks?

Cause 3. Fuel System Issues

The two primary components of your car’s fuel system that can give rise to a rotten egg smell in a car are the fuel pressure sensor/regulator and the fuel filter.

Malfunctioning Fuel Pressure Sensor/Regulator

Fuel pressure sensors or regulators are made to control how much fuel a vehicle utilizes. They also prevent the catalytic converter from overheating or becoming clogged with excess oil. A bad fuel pressure sensor would give your car the wrong signals for how much fuel to transfer into the combustion chamber. This may cause the vehicle to inject more fuel than the cat can handle.

Unprocessed hydrogen sulfide will produce the stench of rotten eggs. It will get back to the engine bay and leak into the cabin. Besides, the catalytic converter may get gummed up after some time. A cat overheats when there is an abnormal buildup of exhaust byproducts in it. This also contributes to the stink and can lead to a fire.

Bad Fuel Filter

Bad Fuel Filter may cause rotten egg smell in cars.

This component acts as a shield that keeps dirt and other contaminants away from the fuel system. It can cause the same issue as a faulty fuel pressure regulator if there’s a blockage or damage.

What to do?

You can resolve a fuel pressure regulator problem by replacing the unit with a new one. And change the fuel filter if it is clogged or damaged.

how to VERIFY your fuel filter is the problem

Bonus: Electric vehicles (EVs) can’t have any of the above issues because they don’t utilize internal combustion engines (ICEs). So you don’t need to worry about such problems if your car is an EV.

How To Get Rid of Rotten Egg Smell in Car?

The best solution is always to make repairs by replacing harmful components. Be prepared to buy a new catalytic converter, transmission fluid, fuel pressure sensor, fuel filter, and other affected car parts/systems. Brace yourself for a possible engine overhaul or replacement.

We should clean every trace of fluid leaks. Air the cabin out by opening all the windows and driving around for a while, using a car air freshener that produces your favorite scent for better results. This will help you forget the irritating stench quickly. Check for other likely factors if the smell persists.

Febreze Air Freshener and Odor Eliminator

Febreze Air Freshener and Odor Eliminator

FunkAway Odor Eliminator

FunkAway Odor Eliminator

VZee Charcoal Bags Odor Absorber

VZee Charcoal Bags Odor Absorber

Treat the situation as a matter of urgency because it could most likely be a serious issue—probably a leak, damage, or malfunction. It would help if you also took care of the problem ASAP because hydrogen sulfide is harmful to human and animal health.

The inhalation of hydrogen sulfide can weaken the respiratory system and the central nervous system. It can also trigger symptoms like skin irritation, dizziness, difficulty in breathing, etc. Long-term exposure will lead to death.

Inspect your problem with an OBD Scanner.

ANCEL AD310 Classic Enhanced Universal OBD II Scanner Car Engine Fault Code Reader

ANCEL OBD II Scanner Car Engine Fault Code Reader 

What To Do If Car Battery Smells Like Rotten Eggs?

Is the rotten egg smell from a battery dangerous?

Yes, If you have a battery that smells like rotten eggs, it’s either because your car’s done nothing but sit for months or years. And the sulfate deposits are building upon the posts, or because one of the cells is shorted out. If it goes away when you start driving, it’s probably just the battery sulfation. If it doesn’t, or if there’s an actual rotten egg smell, you should check the battery. Try giving it a good hard smack (not with your hand), put something metal on all the terminals, and try again. If it’s still acting up, you probably need to buy a new one.

How To Prevent The Rotten Egg Smell?

Implementing preventive measures can save you from the unexpected hassles of dealing with a rotten egg smell in a car. Take the actions below to prevent such a situation.

1. Transmission Fluid Replacement

Change your transmission fluid as at when due (as instructed by the carmaker). A recommended interval is every 12 months. You can target the next refill based on the total distance covered. For example, 60,000-100,000 miles for automatic vehicles and 30,000-60,000 miles for manual vehicles. The interval will depend on how often you use the vehicle.

A black or dark brown coloration means that the fluid should be drained and replaced. It may have dirt, debris, or a burning smell as well. Many vehicles have transmissions that come with “lifetime” transmission fluid. You may never need to replace it throughout the use of the vehicle.

2. Parts Replacement and Servicing

The components and systems mentioned in this guide should be serviced periodically or replaced before they get worn out, damaged, or problematic. A familiar sulfuric smell may disturb your nostrils when you pop your hood open while the battery dies. The smell of rotten eggs will come from the leaking acid or hydrogen sulfide gas of a dying lead battery. Ensure your battery charge doesn’t get too low to avoid this occurrence.

A car battery’s sulfuric acid may trigger breathing problems or lead to thermal or chemical burns. The leak may adversely affect nearby parts or systems as the acid melts through the plastic and metallic components. Add a dying battery to our list of possible causes of rotten egg smell.


Why does my car smell like rotten eggs when I accelerate?

Accelerating your car can produce excess gas in the catalytic converter or exhaust system, which might cause it to smell like rotten eggs.

Car smells like rotten eggs and won’t start. What happened?

If your car smells like rotten eggs and won’t start, you need to get it towed in a hurry. The problem could be worse than a catalytic converter leak. It might mean that your car battery is dead or there has been some other malfunction in the electrical system.

Why diesel truck smells like rotten eggs ?

A diesel truck that smells like rotten eggs may have a bad catalytic converter. This is the part of the system that breaks down hydrocarbons into less harmful emissions, but it can play host to bad gasoline as well. It could be another part of the exhaust system has been breached and now you are smelling hydrogen sulfide in your car.

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