Car Repair and Maintenance

Car Smells Like Rotten Eggs [Causes and Fixes]

If your car smells like rotten eggs, it is generally an indication of a problem with the catalytic converter, regulator, fuel pressure, fuel filter, or old transmission fluid. That said, if the smell only occurs shortly after using the engine at high revs, there is no cause for alarm. However, a lingering sulfur smell requires a thorough investigation. Without further ado, this article discusses the main causes of why your car smells like rotten eggs and how you can fix the issues.

Reasons your car smells like rotten eggs and how to fix

car smells like rotten eggs

It is normal for your car to emit pollutants in order to work properly. However, certain smells, such as the foul smell of rotten eggs, may signal a problem with your car. It can occur whether you have a new or old car, so it’s important to be vigilant and keep an eye (or nose) out for these problems:

  1. Defective catalytic converter

A catalytic converter is a component of your car’s emission system designed to reduce car emissions by limiting the number of toxic gases and pollutants emitted into the atmosphere by the internal combustion engine.

Hydrogen sulfide is one of the many toxic gases that a gasoline-powered car emits. Per the United States Department of Labor, it is extremely flammable and highly toxic. This gas smells just like rotting eggs. If your catalytic converter is stolen, faulty or not functioning properly, it is not converting the odorous hydrogen sulfide into odorless sulfur dioxide. You also want to be sure your cat converter is not clogged up.

How to fix:

If so, you need to replace your faulty catalytic converter. In this situation, your mechanic should replace your faulty catalytic converter, as the additional pollutants in your failing catalytic converter can generate high temperatures that might lead to a car fire.

  1. Failing fuel pressure sensor

This sensor monitors the fuel pressure in your car’s fuel rail and contributes to its fuel economy.

When there is a problem with your fuel pressure sensor, there may be an excess of fuel entering the system. This places additional stress on the catalytic converter, which must process an influx of hazardous gases. Sometimes the catalytic converter is overwhelmed, resulting in the stench of rotting eggs.

Detecting this issue early is preferable for both your safety and your wallet. It would be unfortunate if both the fuel pressure sensor and the catalytic converter were to be replaced. In addition to the smell, several signs could indicate a defective fuel pressure sensor:

  • Check engine light illuminating
  • Having trouble starting your car?
  • Difficulties accelerating
  • Deteriorating fuel efficiency (one tank of gas won’t bring you as far as usual).

How to fix

Simply utilize an automotive scan tool to examine the output specifications of the fuel pressure sensor. Sensor failure without a corresponding engine error code is also rare.

  1. Deteriorated fuel filter

By removing dust and particles, a fuel filter facilitates the fuel’s flow to the engine. Similar to a faulty fuel pressure sensor, a clogged fuel filter can cause the catalytic converter to become overloaded, which can make your car smell like rotten eggs.

While replacing your car’s fuel filter is reasonably inexpensive, replacing a damaged catalytic converter could cost hundreds or thousands of dollars. It is crucial to adhere to a preventative car maintenance routine for this reason. Providing your car with the necessary TLC can prevent larger problems and unpleasant smells.

How to fix

First and foremost, buy a new fuel filter, then go to a professional mechanic to replace the faulty one.

You should replace your fuel filters every two years or 30,000 miles, whichever occurs first. The timeline depends on the manufacturer though. Per the Cars blog, Subaru recommends a replacement after every 60,000 miles while Mercedes commonly recommends replacing a new filter every 30,000 miles. However, most current models recommend replacing it every 150,000 miles or 15 years.

  1. Antiquated transmission fluid

Transmission fluid lubricates the transmission’s working parts and keeps the transmission cool.

You will not absolutely require a transmission fluid change or flush every time you get your oil changed at a body shop. However, a certified car technician must do this service every 30,000 to 60,000 miles.

Sometimes, procrastination literally smells. Delaying essential maintenance could result in old or contaminated transmission fluid, or even worse, fluid that has worn out seals and is spilling onto a hot engine.

How to fix

If you find that you’re running low on fluid, you’ll need to inspect some components to identify the cause of the leak, fix it, and then refill the fluid. To eliminate the rotten egg smell, you may need to replace gaskets and seals in addition to changing the transmission fluid if this occurs.

If transmission fluid is dripping beneath your car, you should contact your mechanic so they can detect and repair the leak.

  1. Damaged exhaust system

The oxygen sensor detects how much oxygen is present in the exhaust system. A damaged oxygen sensor might cause the engine computer to direct an excessive amount of fuel into the combustion chamber. The overly-concentrated fuel will eventually block the catalytic converter, causing the car to smell like rotten eggs.

In addition, a broken or corroded exhaust system can lead to an exhaust leak and the release of untreated exhaust gasses. In addition to producing a repulsive automotive smell, there is a chance that carbon monoxide from your exhaust gases will enter your car.

How to fix

If your exhaust system is substantially louder than usual, open your car windows to prevent the concentration of dangerous gases and contact a professional mechanic immediately. It is best to fix a damaged exhaust system without delay.

  1. Actual rotten eggs

Are you an avid hard-boiled egg enthusiast? Has your teenager been prepping for Mischief Night? Verify that you did not leave any potentially perishable leftovers under the seat by accident.

A rotten egg smell emanating from your car could indicate a major problem that requires prompt inspection by a specialist.

How to fix

If this is the case, remove and discard the eggs and other food items. The offensive smell should then vanish.

  1. There could be a small dead animal

If your car is parked outside, small rodents (mice, rats, and squirrels) may use it as a safe haven, particularly if you do not drive it frequently. These rodents can enter your car’s under-hood area and nest within the air circulation system by climbing up from below the car.

Once they are under the hood, the electrical wiring of your car is at risk of being chewed on.

If one dies of natural causes or is dragged into a ventilation fan, its decomposing carcass emits sulfur compounds that smell like rotten eggs.

How to fix

Simply visit a professional mechanic. Your mechanic will likely disassemble your car’s air intake and ventilation system to remove the animal’s body and all associated debris.

Is it safe to drive a car that smells like rotten eggs

Typically, the smell of rotting eggs suggests that something sulfurous is malfunctioning. That might be hazardous. Therefore, you should not drive a car that smells like rotten eggs.

If the rotten egg smell emanates from an emissions component, it is reasonable to anticipate that you can continue driving for a long time without addressing the issue. Although this may be true for the majority of cars, we strongly discourage doing so.

If the catalytic converter is blocked, it might overheat and catch fire if it gets hot enough. Obviously, this is the worst-case scenario, but it should serve as a reminder not to ignore a rotten egg smell in your car.

Will the rotten egg smell disappear on its own?

Having a car that smells like rotten eggs is not something that will go away on its own. If you don’t take action to resolve the issue, it will simply get worse.

Until you tackle the underlying cause, whether it is forgotten food or a malfunctioning converter, the problem will only worsen.

If you can’t solve the problem yourself, we recommend receiving an estimate and taking your car to a specialist as soon as possible.

Other car smell that indicates a problem

Numerous other car smells can emanate from your car. Some may be pleasant, such as the sweet smell of ethylene in coolant fluid, while others may signify a dangerous gas leak or lead to expensive engine repairs.

It is crucial to take notice if you detect the smell of:

a. Gasoline

If the stench of gasoline persists after refueling, you may have gotten some on your shoes or clothing at the gas station.

A fuel system or vent hose leak could also generate a gasoline smell in your car. This could be an exhaust leak, a potentially hazardous condition that necessitates an expert analysis and treatment by your mechanic.

b. Burning rubber

Typically, a burning rubber smell signifies a loose belt or worn-out rubber hose that is now in contact with a hot engine. A smell of burning could also indicate a blown electrical fuse or worn-out brakes.

If you detect a burning rubber smell, your mechanic should investigate and repair the defective component.

c. Sweet syrup

The sweet aroma of syrup can emanate from a leaking radiator or heating system. This smell is caused by the ethylene in your coolant, and you may detect it while the car is running or shortly after turning it off.

This leak might lead to significant system failure and costly engine repairs. You must have it checked immediately.

d. Musty smell

If you begin to smell the odor of old exercise socks while your air conditioner is running, this is typically a symptom of mildew or mold growth inside your AC.

When you are close to your destination, you should turn off the air conditioning and operate the fan for a few minutes to prevent mildew growth. It promotes the drying of water on the coils of your air conditioning unit and inhibits the formation of bacteria.


If your car smells like rotten eggs, it could be an issue with the catalytic converter, fuel pressure regulator, fuel filter, or even the transmission fluid. Whatever the origin, if you notice a rotten egg smell in your car, take it to a mechanic as soon as possible to have it fixed.

The mechanic will diagnose the problem and repair or replace it before it damages other elements of the engine. If not addressed, this problem might cause your car to break down in the middle of the road.

Latest posts by Bernard Juchli (see all)

Bernard Juchli

Bernard Juchli is an experienced racer, mechanic and team owner who trusts Avon Tyres.Bernard is the lead driver and force behind his Big Dog Garage Race Team. He is the General Manager and Chief Mechanic of Jay Leno’s Garage. Bernard and his crew of seven are responsible for all repairs, restoration and fabrication of Jay’s incredible automobile and motorcycle collection.

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