Car Smells Like Rotten Eggs? (5 Possible Causes)

If your car smells like rotten eggs, there is something wrong with it that needs to be fixed right away. Not only is the sulfur smell harmful to your health, the vehicle can be damaged if this problem is left unchecked.

Reasons Your Car or Truck Smells Like Rotten Eggs

Before reading further, check to make sure you didn’t actually forget eggs in the vehicle a few days (or weeks) ago. That’s probably unlikely, but still a possibility, especially for a chicken farmer!

After verifying the general cleanliness of the vehicle, there are a few systems to check out. The rotten egg smell comes from sulfur gases that get vented into the vehicle from the engine bay, like when you turn on the A/C.

The reason your car or truck smells like rotten eggs can be narrowed down to a few options. Let’s dive into the different possible causes and go over how to identify them below.

See Also: How to Get a Skunk Smell Out of Your Car

1) Fuel System Problems

fuel injectors

Fuel contains hydrogen sulfide, a harmful compound that smells like rotten eggs. In the normal combustion process, the exhaust gases (including hydrogen sulfide) are sent to the catalytic converter in order for some of the more toxic chemicals to be converted to less harmful ones.

Hydrogen sulfide is one of these – it gets converted into harmless and odorless sulfur dioxide.

So when something interferes with this conversion process, exhaust gases including hydrogen sulfide are expelled from the exhaust and sometimes even back up and go back into the engine bay, where they can get back into the cabin.

There are two main components of the fuel system that can cause a rotten egg smell.

Fuel Pressure Sensors

Problematic fuel pressure sensors give the vehicle bad instructions for how much fuel to inject into the combustion chamber. The car can actually inject too much fuel, which means that the unburned fuel goes into the exhaust and gums up the catalytic converter.

In addition to clogging the cat, the hydrogen sulfide in the fuel may escape and cause the rotten egg smell.

Fuel Filter

The fuel filter keeps dirt and other particles which may be present in the fuel from entering the rest of the fuel system. If it clogs or fails it can cause the same problems that faulty pressure sensors would.

If you notice a fuel leak in or around your vehicle that accompanies a gasoline smell, you should get this addressed right away. Fuel leaks are a serious fire hazard.

Related: 4 Causes of Oil Smelling Like Gas

2) Transmission Fluid

automatic transmission fluid leak

If transmission fluid is left for too long without getting changed or if a leak develops in one of the seals in the system, it can start to produce a smell like rotten eggs. Sometimes this happens if the fluid leaks and burns when it comes into contact with the hot engine components.

Leaking transmission fluid poses a fire hazard and can result in skin irritation or respiratory issues if not addressed promptly. It’s important that you check for any obvious fluid leaks and schedule an appointment with a service facility to perform a transmission fluid change or repair the seals.

3) Car Battery

old battery

Lead acid car batteries contain sulfuric acid, a rotten egg-smelling gas. Check to make sure that the battery is not leaking to avoid damage to other components and your health.

A battery can leak if there is a mechanical defect, if it has been overcharged, frozen, or if the battery has some other internal electrical problems.

Some batteries are stored in the trunk or cabin (ie: under a seat). These batteries are usually either sealed or vented. If your battery is not sealed, it may be leaking harmful gases into the passenger compartment. You’ll want to fix the battery venting system as soon as you can.

Related: 5 Symptoms of a Bad Car Battery

4) Catalytic Converter

faulty catalytic converter

Since the catalytic converter is the component that converts the stinky gases into non-stinky gases, it makes sense to check it out. If it’s worn or damaged, it may not be doing its job properly.

The catalytic converter could also be clogged, which is usually caused by combustion problems. Incomplete combustion, for example, sends unburnt fuel into the catalytic converter. It’s not supposed to be there and can actually clog the internal honeycomb pattern so that the catalyst can no longer do its job.

Clogged catalytic converters can be a fire hazard so you should get this addressed as soon as possible.

5) Electrical Issue

If you’re wondering, “why does my car smell like sulfur and burning rubber?”, it may be due to an electrical issue within your vehicle. A faulty component, frayed wiring, or leaking battery can produce sulfuric acid and cause overheating. This may lead to belt or fuse issues, and in worst-case scenarios, even a car fire.

Make sure to monitor your electrical components (including car battery) for signs of damage or leaks and consult a mechanic as needed. If your Check Engine light turns on, it may actually be good news as it may allow you, with the help of an OBD2 scanner, to pinpoint the electrical component that’s the culprit.

Why Does My Car Battery Smell Like Rotten Eggs?

bad car battery

If you’ve determined that the rotten egg smell is coming from your car’s battery, you probably want to know why. This unpleasant odor is due to the emission of hydrogen sulfide gas from the battery.

When your battery goes bad, it can emit hydrogen sulfide, which is often described as smelling like rotten eggs. To add to the problem, this gas is colorless, making it hard to detect.

The reason behind the production of this gas in your car battery is often overcharging. A faulty alternator, charging your batter for too long or at the wrong amperage can lead to overcharging of the battery. This may cause the battery to release hydrogen sulfide gas that smells like sulfur or rotten eggs.

Other than overcharging, another reason for the rotten egg smell is battery acid leakage. When your battery’s acid starts leaking, this signals that the battery is failing. Batteries that emit hydrogen sulfide gas will produce odors similar to rotten eggs or sewer water, which typically happens when the battery gets old and can no longer hold a charge.

Why You Need to Fix the Issue Right Away

First and foremost, it’s very dangerous to breathe or contact hydrogen sulfide. It can cause skin irritation, but it can also depress the central nervous system and respiratory system. This can cause dizziness, coma, difficulty breathing, and other symptoms. There is no known antidote, and prolonged exposure will lead to death.

Sulfuric acid in car batteries can cause severe chemical and thermal burns and difficulty breathing.

As if these weren’t convincing enough, a leaking battery will quickly damage other components in the engine as the acid eats through the metal and plastic.

Also, a catalytic converter that receives too much unburnt fuel can become overheated due to ignition of the fuel in the cat itself, possibly leading to a car fire.

Diagnosing the Problem

Visual Inspection

Start by conducting a visual inspection of your car to identify any potential causes for the rotten egg smell. Clean out the entire interior, checking for any spoiled food or other sources of the odor. At the same time, you can also vacuum and clean off the seats.

Under the hood, examine your car battery for any leaks or signs of damage, as lead-acid batteries contain sulfuric acid, which can produce the smell we’re trying to get rid of. If you notice any issues with the battery, it’ll need replacement right away.

Also, pay attention to the condition of your transmission fluid. If it has been left unchanged for too long, it’s possible that’s your problem. Check for any leaks and ensure the fluid is at the proper level.

Professional Diagnosis

If the interior, battery, and transmission fluid seem normal, it’s time to consult a professional mechanic, as there might be issues with your vehicle’s fuel system, catalytic converter, or electrical component.

Your mechanic will likely start by checking for any stored trouble codes with the help of a diagnostic tool. This will help pinpoint the source of the problem, especially if your check engine light is on.

For example, a faulty fuel pressure sensor might be sending too much fuel into the system, clogging up the catalytic converter, which can cause a rotten egg smell. A skilled technician can identify and fix this issue to ensure your car is running efficiently.

How to Remove a Rotten Egg Smell From Your Car

Once you’ve diagnosed the problem, it’s often not difficult to remove the rotten egg smell from the vehicle. Any of these components need to be replaced if found faulty. Repair of any of the parts is not an option.

Once the problematic part has been replaced, the smell should go away on its own fairly quickly if you allow the cabin to air out. Open all windows and drive around for a while and see if the smell persists.

If the smell won’t go away, you may have another component that is behind the smell. It’s unlikely, but not impossible, for two separate causes happening at the same time.


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