It’s hard to believe that a simple, everyday object like a car smells like farts and can cause such a stink.
Today’s cars have become so technologically advanced that they are nearly impossible to produce stinky odors. But even though the new vehicles may be odor-free, they still emit stinky and nasty sulfurous odors if something is wrong with the components of the engine, mainly the exhaust system. The most common of these odors is the one that you are probably smelling right now—the stench of a fart.
In this guide, I’ll highlight some of the most common causes of fart-like or rotten egg smell in your car’s interior.
Table of Contents
Causes of Car Smells Like Farts
Here are some of the most common causes of cars smelling like fart.
1. Animal Trapped in Engine Bay
If animals like birds, rats or rodents are trapped in the engine bay, they may cause a fart-like smell in the car. One possibility is that the rat could be dying and decomposing in the engine bay, which would obviously cause an unpleasant smell. Another possibility is that the rat could have gotten into the car’s exhaust system and is now trapped, which would also cause an unpleasant smell.
Rat is a nocturnal mammal and the only way it can survive in the daytime is by burrowing itself into the engine bay for warmth. The rats usually get trapped behind the battery. They chew the wires and then get stuck between the hood and the battery. The heat from the engine causes the rat to release a foul-smelling gas which creates a bad fart-like smell in the car.
A bird can also get caught in the bumper and get sucked in through the brake duct vents.
You should spot dead animals near your vehicle’s radiator fan belt, under the car seats, cabin air intake system, cabin air filter, and heater blower. You can use Ozium spray to get rid of any stinky smell in your car. Spray the Ozium spray in the air vents and the air intake that’s at the bottom of the windshield. Blast the air, AC, and heater for a couple of minutes each. It will help eliminate the fart-like smell from the car.
2. Molds and Mildews In The AC Vents
If the car smells like farts when the AC is turned on, it means that it is due to molds and mildews growing inside the air ducts of the car.
Molds and mildews grow in damp, dark places like the AC vents in your car. These are caused by moisture and air circulating through the vents. This can cause unpleasant odors.
The moisture develops due to the condensation of air inside the AC ducts. It has to be drained from the system. But sometimes, drains are plugged and the condensate starts leaking into the car cabin, causing a fart-like smell. You can read my guide on car AC smells like vinegar to get more details.
If the fart-smell in your car is coming from AC vents, always turn off the car AC a mile from home and leave the fan on. This keeps air moving through the air ducts and helps prevent moisture build-up that leads to mold and mildew.
Moreover, to kill molds and mildews in AC vents and fix the fart-like smell in your car, take Lysol spray and spray it into the vents in front of the windshield. Lysol spray will kill 99% of bacteria and molds in the car vents. Moreover, the Lysol spray will also remove any organic material stuck and clogged in the vents.
Moreover, you should also replace the cabin air filter as dust particles in the cabin air filter can also cause a rotten egg smell in your car’s cabin.
3. Plugged Catalytic Converter
A plugged catalytic converter can cause a “farts-like smell” in a car because the converter is not able to properly convert exhaust gases into less smelly compounds. It especially happens when you accelerate your car.
There are a few different things that can cause a catalytic converter to become plugged. One is simply age and wear. Over time, the catalytic converter can become contaminated with gasoline, a build-up of carbon, and other materials, which can restrict the flow of exhaust gases.
A plugged catalytic converter can cause a car to emit a foul-smelling gas due to the build-up of unburned fuel in the exhaust system. This can happen if the converter is not operating properly or if the engine is running too rich.
The catalytic converter is responsible for oxidizing carbon monoxide and unburned fuel into carbon dioxide and water vapor. If the catalytic converter is plugged or the air/fuel mixture is too rich, the catalytic converter couldn’t convert all of the additional fuel in the exhaust. As a result, a foul odor with a rotten egg, and sulfurous smell is produced.
If your car is running fine when having a fart-like smell, the symptom is probably normal. If the car also has a running problem and you can see the check engine light on the dashboard, you should immediately stop the vehicle and pull the trouble codes using the OBD2 scan tool.
4. EGR Valve Is Gunked Up
The EGR (Exhaust Gas Recirculation) valve regulates the flow of exhaust gas to the intake side. When the EGR valve is open, a small amount of gas is allowed to pass into the intake side. If the EGR valve is gunked up with the soot in the exhaust gases, it will cause the sulfur smell because of incomplete combustion. The error codes related to the EGR system will be P0400, P0401 or P0402.
5. Coolant Leak
A coolant leak can cause a fart smell in a car because the coolant can interact with the car’s exhaust system, causing it to vaporize and produce unpleasant odors.
The vaporized coolant can then be drawn into the car’s cabin through the ventilation system, giving off a fart-like smell.
A coolant can leak through the heater core, radiator, radiator hose, and a cracked air-intake manifold gasket.
If the carpet on the passenger side under the dashboard is wet, it could be the heater core leaking.
If your engine is overheating or the coolant level is too low, it means that the coolant is leaking.
6. Bad Fuel Pressure Regulator
If the fuel pressure regulator is not working correctly, it can cause the fuel to be pushed through the system too quickly. This can cause the fuel to build up in the engine and create a fart-like smell.
A bad fuel pressure regulator causes high pressure of fuel, due to which it injects in the combustion chamber with a heavy amount. As a result, the mixture runs rich. A bad fuel contains a good amount of sulfur, which produces hydrogen sulfide during combustion. This causes a rotten egg and fart-like smell in the car.
7. Bad Fuel Injectors
The main function of the fuel injectors is to introduce the fuel into the engine cylinder under high pressure and in a certain amount so that it can be efficiently burned with the air.
Fuel injectors spray fuel in the atomized form so that it thoroughly mixes with the air to form a uniform mixture. When fuel injectors become bad, they inject unwanted fuel into the cylinder, due to which the combustion mixture runs rich. Moreover, when seals around the fuel injector degrade over time, fuel leaks through the fuel injector and produces a noticeable fart-like smell.
To learn how fuel injectors get bad, you can read my guide on car won’t start after replacing fuel injector.
8. Exhaust Leaks
Smelling gas fumes inside your car indicates exhaust leaks. This is because exhaust fumes contain sulfur, which can smell like sulfur dioxide. When there is a leak in the exhaust system, these fumes can escape and enter the car, causing it to smell like farts.
An exhaust leak can be due to a cracked muffler, clamps, or a damaged exhaust pipe. As you drive, exhaust gases make their way to the car’s cabin and give an unpleasant odor. If the exhaust gas is leaking before the muffler, it will produce a rattling and rumbling sound as the muffler is responsible for dampening the noise of the exhaust.
To detect exhaust leaks, take a shop vac and plug its end that blows air into the tail pipe. Open the hood and see if anything is coming out of the manifold. Make sure the engine is off. Also, make sure that the exhaust system is cold. During this process, use a soapy water bottle to check for bubbles at the loose connections of the exhaust system.
9. Puddle Of Water In A Spare Tire Spot
A puddle of water in a spare tire spot can cause a fart-like smell in your car for a number of reasons. First, when water mixes with the dirt and grime in the tire, it can create a foul-smelling concoction. Second, if the water is stagnant, it can start to develop bacteria, which can also lead to an unpleasant smell. Third, if the water is left in the tire for a long period of time, it can start to break down the rubber, which can also release unpleasant odors.
If your car has a sunroof, water can leak through the sunroof and pool up in the spare tire area due to a clogged drain of the sunroof. You can read my guide on water dripping from under steering wheel to learn more about leakage from the sunroof.
You should also check the weatherstripping around the trunk as the water can also leak through it and make a puddle in a spare tire well. A sugru at the end of weatherstripping might work.
Also, if the hatch door of the tailgate is misaligned, water can also leak through it and create a pool in a spare tire well.