If you’ve ever washed and detailed your car, you’ve probably faced a moment a bad smell might arise from the vehicle, especially if you have a mechanical failure.
If you smell a rotten egg odor in the car, that means there’s something that needs your attention. You need to respond quickly; worse than a horrible smell in the car is potentially dangerous mechanical problems that need to be addressed.
In this article, we’ll go over some of the reasons why your car smells like rotten eggs to help you troubleshoot the issues. We’ll touch on some miscellaneous bad smells that tell you something is mechanically wrong, then answer some FAQs.
Causes for Rotten Egg Smell in Car
Most of the time a rotten egg smell is due to a bad catalytic converter, but it could also be caused by an alternator with a bad voltage regulator, bad battery, or bad transmission fluid. That said, never rule out a dead animal or an actual rotten egg inside the vehicle.
Here’s some more detail on what could cause a rotten egg smell in your car:
#1. Bad Catalytic Converter
The number one cause of whatever is inside your car smelling like rotten eggs is most likely due to the catalytic converter failing. Catalytic converters are necessary components to convert harmful chemicals released from the engine into harmless chemicals.
When the catalytic converter becomes clogged or no longer works properly to continue the chemical reactions, you will start to smell rotten eggs while driving. The rotten egg smell is due to sulfur dioxide being emitted from the exhaust.
Also, when the catalytic converter fails, you will be releasing harmful gases into the atmosphere. A Check Engine Light will illuminate and your car may fail an emissions test.
#2. Defective Car Battery.
Sulfur smells may appear if the battery acid leaks. If the battery is leaking, it indicates the battery is bad.
Batteries that emit hydrogen sulfide gas will smell like rotten eggs, or sewer water. This smells occurs when a battery is old and cannot hold a charge.
#3. Overcharging Alternator.
The alternator charges the car battery anywhere between 12.5 and 14.8 volts, depending on the car model. But if there is an issue with the alternator or voltage regulator, it can charge the battery at more than 15 volts.
When the alternator overcharges the car battery, it makes it “boil” the battery acid which emits a rotten egg smell. This is also dangerous due to the risk of the battery exploding.
#4. Old Transmission Fluid.
If you have a car with an automatic transmission, you must ensure that you change the fluid regularly. If you do not, the fluid can become old and cause problems. The seals will not be lubricated, and a leak can occur.
Fluid will leak and have a variety of smells, but some people report it smells like rotten milk or rotten egg. To eliminate this problem and maintain transmission health, change the fluid, and change gaskets and seals.
#5. Dead Animal.
Up to this point, you could always blame the smell on mechanical failure. That is because that is the most common reasons for rotten egg smell. At the same time, you should try to not overlook some familiar conditions.
If you have had a mouse or some other animal get into your HVAC or exhaust system, you can also smell something rotting out. These situations happen more often during colder weather or if you have stored your vehicle for any length of time.
If you start up the engine, you may kill the animal if it can’t escape. Then as the body decays, you are going to get a smell.
#6. Rotten Egg.
Now, above, we told you that a rotten egg smell could come from a variety of sources in addition to an actual rotten egg. We sincerely hope you do not have groceries rotting in your vehicle, but it could happen, especially if it rolled under the seat or into a crevice.
You can avoid these challenges by simply cleaning the inside of the car. Not only will it look nice on the inside, but you will also avoid the terrible odor in the first place.
How to Fix Rotten Egg Smell in Car?
#1. Check the Vehicle.
If there is no Check Engine Light, you will want to start by inspecting the vehicle. Completely clean the interior of the vehicle and see if you can find any spoiled food. During the process, you might as well vacuum out and clean off the seating too.
If you find nothing in the car, then take a good sniff outside the car to try to distinguish where the odor is coming from. If you can identify a specific location where the smell is present, then the problem may be a dead animal in one of the systems. You will need to remove this animal if you want the smell to go away.
Depending on where the animal traveled, you may need to remove parts in order to access it. If you don’t know what you are dealing with, then take it to a professional.
#2. Test Alternator and Battery.
As mentioned, a bad or overcharging alternator or battery can cause your car to have a rotten egg smell. Therefore, you want to measure the alternator to ensure that it is not overcharging.
Now, you will want to check the condition of the car battery to ensure it is working properly. If you see something wrong with the alternator or battery, then they need to be replaced.
#3. Scan Trouble Codes
When the Check Engine Light is illuminated, it indicates that there is something mechanical happening. First, hook up the code scanner to see what the issue is.
If you do not have a code reader, go to your local auto parts store for a free scan, and research the trouble codes to see if it points you in the right direction.
If there are lots of trouble codes, it is often easier to delete them and take the car for a drive again until the light comes on. After rescanning it, you will have a better idea of what the issue actually is.
If there are any trouble codes related to engine performance, it may cause the catalytic converter to fail, and this needs to be fixed before replacing the catalytic converter.
#4. Check Transmission Fluid.
If it’s been a while since you had your transmission fluid changed, pull out the fill plug and smell the fluid. If it smells burnt or unpleasant, it’s probably time to change it anyway.
Then, change the transmission fluid and run the car again to see if the smell goes away after driving it. If you have a leak, you will want to fix this before replacing the fluid.
#5. Do the Repairs.
Now that you know what is wrong with the car, it’s time to repair the issue. The good news is that with some issues, you can fix these issues at home.
For example, if the battery is old, you can probably just replace it yourself. If not, most auto parts stores will replace it free of charge if you buy the battery there.
Changing a catalytic converter typically isn’t very difficult but is very expensive. The repairs you may do should not cost nearly as much.
Additional Car Smells That Are Alarming
#1. Burnt Oil.
No one enjoys the smell of burning oil, and it usually means the oil is overheating or leaking onto something that gets hot, like an exhaust. Pull out the oil dipstick and take a whiff. Inspect the system for any leaks or signs of leaking and repair it before filling the system.
Burning transmission fluid can also smell the same, so check this as well. If the transmission or oil are overheating, you are endangering these vital components from failing.
#2. Gas.
It’s completely normal to smell gas when you’re filling up at the gas station, but you should experience this smell quickly dissipate after you leave. If you notice that it is lingering on, then you could have a problem on your hands.
First of all, you’ll want to determine whether you really did get gas spilled on the car or your clothes, if so, you’re going to want to clean it right away! When you’re done dealing with that, think about whether you have an actual fuel leak in your vehicle. You don’t want to keep driving it with a leaky fuel system and risk a vehicle fire.
#3. Burning Rubber.
Your car’s belts and hoses are rubber. If either is disconnected or laying against a hot component melting can occur.
Burning odors can develop from the electrical part of your car also with many of the same odors as your vehicle’s belts or hoses. You could have a burnt fuse or another significant electrical component. For your safety, you need to identify what is burning before continuing to operate your vehicle.
#4. Sweet Odor.
If antifreeze is leaking, it will smell sweet like syrup. Coolant can leak from the heating system or radiator.
Coolant is toxic for kids and pets, but it is desirable because of the smell, and that is one reason to fix the leak right away.
Is a Car That Smells Like Rotten Eggs Safe to Drive?
If your groceries are causing the smell, you can continue to drive without worrying about danger. However, if it’s mechanical failure, specifically an overcharging alternator or faulty catalytic converter, you should address the issue immediately.
If the problem is low transmission fluid, then you are continuing to allow further damage to your car by not fixing the situation.
How Do I Stop My Car from Smelling Like Rotten Eggs?
If the smell is coming from a car part, then you need to fix the part. That is the only way you will have a solution to the issue; otherwise, clean your car out and make sure you dispose of whatever is causing odor before it permeates the entire cabin.
What Does it Mean When Car Exhaust Smells Like Rotten Eggs?
In most cases, this is an indication that the catalytic converter has gone bad. Without the chemical reaction taking place properly, you’re left with the sulfur odor. You may also be experiencing an overheating alternator, bad transmission fluid, or rotting food or animals. All these issues can be cleaned or repaired to remove the smell.
There is no reason to continue living with the rotten egg odor in your car. If cleanliness is your issue, a quick and easy cleanout can take care of this for you. A cleanout can also assist you in finding that dead animal that is rotting inside the system.
If the odor is from a mechanical issue, you may need to have the repair performed. If you have the tools and know-how, you complete the repair in your home garage.
Otherwise, you can reach out to a professional. I am sure you will be happy that the smell is gone and your car is running better because you took the time to improve it, avoiding future mechanical issues as a result. The sooner you diagnose and repair the issue the lower your chance will be that you will have more serious issues down the road.