Car Smells Like Farts (9 Potential Causes)

Got a funky odor in your car that’s got your nose wrinkled? I feel your pain. Foul smells can make driving uncomfortable and leave you holding your breath.

But don’t panic yet. In this guide, we’ll explore some common causes of fart-like odors in vehicles and provide tips to get your car smelling fresh again.

Some Key Insights for You
  • Animals like rats getting trapped in engine bay can cause fart smell from decomposing or getting stuck in exhaust
  • Mold and mildew growing in moist AC vents also creates fart odors when circulated
  • Plugged catalytic converter unable to properly convert gases causes rotten egg smell
  • Gunked up EGR valve causes incomplete combustion and sulfur smell
  • Coolant leaks interacting with exhaust creates fart smell in cabin
  • Bad fuel pressure regulator or injectors cause rich mixture and fart smell
  • Exhaust leaks allow sulfur fumes to enter cabin smelling like farts
  • Stagnant water in spare tire well creates bacterial buildup and fart odor

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.

How to fix?

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.

How to fix?

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. It will also remove any organic material stuck and clogged in the vents.

In addition, 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.

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 can’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.

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. 

How to detect?

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. It’s very important to diagnose common check engine light issues.

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 a sulfur-like smell because of incomplete combustion. The error codes related to the bad 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 air-fuel 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.

How to detect?

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

puddle of water in a spare tire well also causes fart-like smell in car

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.

Some First Hand Experiences Shared By Users In Different Forums

Our team conducted research across various online communities, forums, and subreddits to gather user comments and opinions on “car smells like fart”.

User 1 says:

Had a weird moment with my ’07 Honda Fit. Started smelling like farts every time I turned on the A/C. I was baffled. Turns out, the cabin air filter was super old and moldy. Replaced it and boom, fresh air again!

User 2 says:

I drive a 2013 Fiesta. Started getting a fart smell every time I hit the gas. After some online searching and checking under the hood, I realized it was an exhaust leak near the engine. Fixed the gasket and no more stink.

User 3 says:

My Jeep Wrangler started smelling like farts out of nowhere. I discovered it was due to water leakage and subsequent mold growth under the carpets. After drying it out and cleaning with a mold remover, the smell was completely gone.

User 4 says:

My Subaru Outback had a fart-like smell that was really bothersome. After some digging, I found that the rear seat cushion had absorbed water from a spilled drink, leading to mildew. Cleaning and airing out the cushion helped eliminate the smell.

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