8 Reasons Why Your Car Smells Like Rotten Eggs (And How to Fix It)

There are a few possible reasons why your car smell like rotten eggs. Let’s look at what could be causing the unpleasant smell, and maybe more importantly, how to fix it.

What Does a Rotten Egg Smell Indicate?

The rotten egg smell that people describe is often the result of hydrogen sulfide gas. Sulfur by itself is odorless, but hydrogen sulfide is a distinct and unpleasant odor.

If you’re detecting a rotten egg smell, and you’re not in traffic behind an overflowing garbage truck, something may be wrong with your car.

Different Rotten Egg Smell Scenarios in Cars

A few scenarios can cause a rotten egg smell when you’re driving a car.

1) Rotten Egg Smell in Car When Accelerating

If you smell rotten eggs when you accelerate, it might be due to an issue with the fuel system.

Possible Cause

Gasoline contains sulfur, though the EPA limits the total allowable amount in fuel. Sometimes, the fuel we purchase for our car might exceed the federal limit due to a manufacturing issue, old gas in the tanks at the filling station, or even malfeasance.

Regardless of the reason, if the tank of gas has too high a concentration of sulfur, it may result in excess sulfur dioxide in the exhaust.

The same thing can happen when the fuel is OK, but the fuel pump or sensor isn’t working correctly.

How to Fix It

The easiest way to fix the issue of excess sulfur in your fuel is to tolerate the smell until you burn up the tank of fuel a bit and replace it with better gasoline.

If the fuel system is the culprit or the sulfur concentration in your fuel is too extreme to drive with, you’ll have to drain the system. Then you can change the fuel pump and fuel sensor, too, if necessary.

2) Car Smells Like Rotten Eggs and Won’t Start

If your vehicle won’t start and you detect the smell of rotten eggs, there might be a simple cause.

Possible Cause

There is usually sulfuric acid inside of a car’s battery. When the battery is working right, the car starts normally, and you don’t smell anything. But if the battery has cracked, shorted out, or failed, it may leak some sulfuric acid. That will result in a foul smell and cause trouble.

How to Fix It

To fix the issue, first, confirm the battery is the source. Locate your car’s battery. It’s probably under the hood, but some manufacturers put it in the trunk.

Now take a sniff and see if the sulfurous smell is coming from the battery. If it is, remove the battery lugs from the top of the battery and lift them out of the car.

Reinstall a new battery. Remember to recycle the old one.

3) Car Smells Like Rotten Eggs When Starting?

If your car starts up, but it leaves you with a nasty rotten egg smell, you might have an issue with the battery or the exhaust system.

Possible Cause

The catalytic converter on a car is part of the exhaust system, and it helps convert the hydrogen sulfide byproducts of combustion into odorless sulfur dioxide.

If you only smell rotten eggs after you start the car, the converter could be failing. Or, your battery may be leaking, but it hasn’t affected your startup yet.

How to Fix It

Use your sniff detector, also known as your nose, to try and pinpoint the source. If the smell is coming from the battery, change it. If it is coming from the exhaust, you may want to bring the car to a mechanic.

Keep in mind that catalytic converters are a hot commodity and are stolen routinely. Make sure that no one has tampered with your car in an attempt to steal the converter.

4) Car Smells Like Rotten Eggs and Shakes?

This is a problem that could come from a few sources.

Possible Cause

If your car is shaking, it might be because there is a problem with the fuel. That can be because of bad gas, a bad fuel pump, or a bad sensor.

How to Fix It

Try adding some high-quality gas to a partially depleted tank to fix this. If that doesn’t work, you’ll want a mechanic to look at the car.

5) Car Smells Like Rotten Eggs Check Engine Light On?

If the check engine light (CEL) is on, your car might have an issue with the exhaust system.

Possible Cause

If the car has a code for a catalytic converter issue, it will illuminate a light on the dashboard.

How to Fix It

The only way to fix a non-working catalytic converter is to replace it. If it’s working but really dirty and fouled with deposits of sulfur, you might be able to burn off some of the deposit by driving for an extended period.

6) Car Smells Like Rotten Eggs When Heat Is On?

If the air coming out of your car’s heater vents smells sulfurous, you should check it out immediately.

Possible Cause

You might have a leaky exhaust system or a failing catalytic converter.

How to Fix It

Check your exhaust system for leaks, and consider replacing the catalytic converter.

7) When Car Battery Smells Like Rotten Eggs

A car battery that smells like rotten eggs needs replacement.

Possible Cause

If the battery in your car has cracked, shorted out, or failed, it may leak some sulfuric acid. That will result in a bad smell, and you’ll also likely have starting trouble.

How to Fix It

Never jump-start a leaking battery. Remove the battery lugs from the top of the battery and lift them out of the car. Reinstall a new battery.

8) Car Smells Like Rotten Eggs When Off?

You can mostly eliminate the exhaust system from your list of likely suspects if it smells when the car isn’t running.

Possible Cause

The most likely cause is a leaking battery.

How to Fix It

Replace your battery.

How to Get Rid of the Smell After Fixing the Issue

After you’ve repaired the issue causing the rotten egg smell, it will usually dissipate on its own.

If you think it’s lingering a bit, consider going for a drive with all the windows down. Cycle the air conditioner and the heater a bit to get the smell out of the vents too.

Is It Safe to Drive a Car That Smells Like Rotten Eggs?

The smell of rotten eggs usually means that something sulfurous isn’t working right. That can be dangerous. So, you shouldn’t drive a car that smells like rotten eggs.

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Author: DJ

Dave Junior is a hands-on automotive technician with experience in performing service, diagnostics, and repairs on domestic and imported vehicles. He enjoys writing and sharing his knowledge far and wide.

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