An exhaust smell in your car can come from several sources: an exhaust leak, a faulty catalytic converter, or a bad heater core. Smelling exhaust in your vehicle while driving, idling, or both is not normal and should be investigated right away.

A functioning exhaust system should direct away harmful gasses coming from your engine, so if you notice an exhaust smell inside the cabin of your car, it’s likely that something is amiss.

Aside from the unpleasant smell, car exhaust gasses can expose you to carbon monoxide poisoning. That said, it’s imperative that you take some time to suss out the problem before you continue driving.

Here to go through the most common reasons you may be smelling vehicle exhaust while driving or idling is

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Why is there an exhaust smell in your car?

When you catch that first smell of exhaust, your first reaction may be to assume it’s nothing. Maybe your nose got a quick whiff right as you began to accelerate or maybe you didn’t smell it until you were idling at a red light. Whatever the circumstance, you don’t want to risk breathing in toxic exhaust fumes longer than you have to.

To avoid mixing your oxygen with too many emissions, you’ll first need to identify which car component is unable to do its job and leaking exhaust into your vehicle. Let’s go over some of the most common reasons for an exhaust smell in a car.

MORE:

What to do if there’s smoke from the engine or exhaust

Faulty catalytic converter

The catalytic converter is a key component in any car’s anti-pollution system. It’s like the middleman between the harmful compounds emitted by the engine and the exhaust pipe that kicks out gaseous waste. Its job is to convert all those harmful gasses into less harmful gasses before exiting the tailpipe.

Your catalytic converter can become clogged, contaminated, overheated, or just worn down over time, and any of these problems will impact its function. If you suspect a failing catalytic converter, you’ll need to take your vehicle to a mechanic or service center for a part repair or replacement. It is illegal to drive without a functioning catalytic converter.

Bad heater core

Another common cause of an exhaust smell in a car is a bad heater core. The heater core is a part of your vehicle’s coolant system and, if damaged or faulty, can leak exhaust into the car’s cabin.

You’ll know if the heater core is responsible for the exhaust smell if any

antifreeze

puddles form under your car after it’s been parked for some time. You’ll likely be dealing with a poor seal within the heater core that needs to be replaced if this is the problem.

Exhaust leak

A general leak in the car’s exhaust system can also cause that unpleasant and dangerous car smell, though it is a bit harder to diagnose.

The exhaust system of your vehicle is sizable and includes plenty of components so pinpointing the exact location of the leak will take some work—probably best done by a professional.

A good indicator of an exhaust leak causing the exhaust smell in your car is louder engine noise. A more prominent roar will be noticeable when you cold-start your vehicle and when you press on the accelerator.

Understand the type of exhaust smell

You’ll want to address any out-of-place exhaust smell as soon as possible to avoid lasting consequences. Any repair will be easier to deal with if you can first identify what the smell is.

Gasoline smell

If you’ve been driving or simply around vehicles for any amount of time, you’re likely familiar with the smell of gasoline. That pungent, sharp scent may be infiltrating your car’s cabin from something as simple as a cracked fuel cap—or something more involved, like an imbalanced rich air/fuel mixture in the engine or faulty fuel injectors.

Black smoke billowing out from your muffler may also accompany the gasoline smell, so keep your senses out for that.

Regular exhaust smell

Regular exhaust smell has a musty, smoky scent to it. If you catch a burning smell not paired with any other particular scent, it’s likely you’re smelling regular exhaust from a damaged exhaust system.

Smell of rotten eggs

Catalytic converters remove sulfur—otherwise known as the rotten egg stink—from the exhaust gasses before they exit your vehicle.

A damaged catalytic converter won’t be as effective in that removal and can thus produce a noxious cloud of egginess that may permeate your car cabin.

Sweet-smelling exhaust

If the exhaust smell you're dealing with has a hint or more of sweetness to it, you could have a damaged cooling system. Antifreeze has a distinctive sweet-smelling scent that can be helpful in identifying this particular problem within the exhaust system.

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What to do if you smell exhaust fumes in your car

As we’ve previously mentioned, exhaust fumes are dangerous to inhale. But that doesn’t mean you need to shift into panic mode as soon as you catch a whiff. Instead, find out where the exhaust fumes are leaking from and what you can do to fix the issue.

Identify the smell

Identifying the exact smell of the exhaust will go a long way in helping you diagnose the problem. Is it eggy or sweet? Musty and hot or sharp and pungent? Take detailed notes of the offending smell to make the repair process simpler.

Determine the source of the problem

After you’ve identified what the exhaust smells like, you should have an easier time determining the source of the problem.

First and foremost, make sure the smell isn’t coming from another vehicle around you. It’s possible for another vehicle’s exhaust to enter your car through your HVAC system or open windows, so ensure it’s your vehicle producing the smell. Then, link the scent to its respective problem.

That rotten egg smell discloses damage to your catalytic converter. If it smells like gasoline, have your fuel system checked over. A slightly sweet scent and puddles under your car point to a coolant problem.

Check window and door seals

The smell of exhaust is around us all the time while we drive, but it won’t necessarily be able to get into our cars’ cabins until something malfunctions. One of those malfunctions could manifest as loose or damaged window and door seals.

Naturally, the seals around a vehicle’s windows and doors break down and decay over time. If you notice an exhaust smell while all windows and doors are shut, check the seals around your vehicle to make sure they aren’t allowing harmful emissions to infiltrate your cabin.

Take your car to a mechanic

The best way to know for sure what you should do about the exhaust smell permeating your car’s interior is to bring your car to a certified mechanic as soon as you start smelling it.

With up-to-date diagnostic technology and invaluable working experience, a professional mechanic should be able to pinpoint the problem and offer solutions to remedy it.

If the exhaust smell is really bad, you may wish to have your car towed rather than driving it and risking carbon monoxide poisoning or other further damage.

Inhaling these fumes for too long can cause you to lose consciousness—an obvious hindrance to safe driving—so it’s always better to be safe than sorry.

MORE:How to decide if you should take your car to a repair shop or a mobile mechanic

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How does an exhaust system work?

Exhaust manifolds take air in from multiple sources and combine them in one pipe. Then, oxygen sensors read the oxygen-to-exhaust ratio to tell the fuel system how much fuel to direct to the engine.

The catalytic converter then converts the waste product gasses to carbon dioxide, and the exhaust gases are released out of the muffler.

What is the first thing to check when a car has an exhaust smell?

The first thing you should do when you smell exhaust in your car is to identify if the smell is coming from your car or another car around you.

It could be coming in through your HVAC system or an open window, especially if you’re sitting in heavy traffic or at a stoplight.

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