How to Diagnose Car Smells

Three Methods:Diagnosing Exhaust, Sulfur, and Gas SmellsDiagnosing Burning SmellsMaking Your Car Smell Better

If you're smelling something unusual in your car, this can be the sign of a serious mechanical problem. It also might just mean that you spilled food in your car and have a mildew problem, though. Either way, it's important you diagnose and eliminate any car smells. Some of them can be very dangerous.

Method 1
Diagnosing Exhaust, Sulfur, and Gas Smells

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    Determine whether you have a leak in your exhaust system. Smelling exhaust in a car is an incredibly dangerous situation because carbon monoxide is toxic for human beings. So if you smell exhaust within your car, get the car checked out by a professional immediately.
    • There could be a hole in anything from the muffler to the tailpipe of your car.
    • It’s also possible that exhaust is leaking into the car through a part of the interior that is worn. Don’t play around with this scenario. It’s extremely dangerous.
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    Replace your catalytic converter. If you smell a sulfur or rotten eggs smell, you’re probably going to need to get your car serviced by a professional.[1]
    • Usually, the smell of sulfur indicates there is a problem with your catalytic converter. The converter will probably need to be replaced.
    • The way this is done is to cut the converter on both ends after the engine cools. Then, replace it with a new converter.
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    Replace your fuel filter. It’s also possible that the converter is just plugged up, but most likely you are going to have to replace it.
    • Other causes of rotten eggs smells can include hot engines or broken fuel pressure regulators. All you might need to do for the latter is replace your fuel filter.
    • A rotten eggs smell is probably the result of hydrogen sulfide. Sulfur is present in gasoline, and it’s converted to sulfur dioxide, which is odorless. However, when your converter breaks down or its filtering layers are worn out, sulfur produces a strong smell of rotten eggs.[2]
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    Determine whether you've flooded the car. Gasoline smell signals a problem with the car. However, it might be easy to fix if the car is just flooded.
    • If the car isn’t starting, flooding is a distinct possibility. Just wait a few minutes, and try to start the car again.
    • If the gas smell seems to be emanating from underneath your hood, your fuel injection system or carburetor might be leaking fuel. You can also check your fuel pump for a streak of leaking gasoline, which should be clearly visible.
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    Check fuel lines and hoses. You will also want to check the fuel lines and hoses inside your hood that lead to the fuel tank. It’s possible they’re disconnected or rotted.
    • You might want to check under the hood again after parking the car overnight. You will want to look for stains because gasoline evaporates pretty quickly.
    • Make sure not to smoke cigarettes while looking for gasoline leaks. This can be very dangerous. It’s also possible that you spilled some gasoline while pumping it into your car. Maybe the gasoline you smell is that which dropped onto your hands!

Method 2
Diagnosing Burning Smells

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    Lighten up on the clutch and brakes. If you smell burning toast while you’re working the gears of the car, this is probably an issue with your clutch. But it could also be your break pads.
    • You could be riding the clutch pedal too hard, which creates friction between the clutch facing and the clutch slips. If you lighten up on it, the smell should disappear. The material is made of paper, which is why the smell has the faint odor of burning paper.
    • If you’re pressing your brakes too hard, you might be overheating your brake pads. This can also cause a burning smell. It could help to downshift. You also could have a dragging brake because a brake caliper piston might have seized. Another possibility is to make sure you didn’t leave your handbrake on while driving.
    • One way to check the brake pads is to see if any of your wheels feels hot. If none of them does, then maybe it's the overheated clutch instead of a dragging brake shoe.
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    Check to see if your engine is overheating. Figure out why you smell oil burning. Burning oil has an odor that is thick and acrid. When you smell it, you need to determine right away whether you are running out of oil.
    • Another possibility is that your engine is overheating. If neither one of these things seems to be the answer, check to see if there is oil leaking onto your engine block. You may need an oil change if you are smelling burning oil.[3]
    • You could also check your transmission fluid using a dipstick. Maybe your transmission fluid is low. This can cause it to burn in the transmission because the gears get too hot because they are not properly lubricated.
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    Check for a loose hose. If the smell is closer to rubber burning than oil burning, check to see if a hose came loose under your hood.
    • It’s possible that it’s touching a part of the hot engine. Sometimes an oil smell is from a leaking crankshaft seal.
    • If that’s the case, you’ll also find oil on the pavement beneath the car most likely.[4]
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    Check to see if your coolant is leaking if you smell maple syrup. If the car smells like maple syrup after you’ve warmed up the engine (or even after you’ve shut it off a few minutes later), you should take immediate action.
    • This smell might mean that your coolant is leaking from somewhere like a radiator or heater hose. This kind of a problem means it's a good idea to take your car into a professional.
    • If you smell maple syrup outside the car, this might mean that you have a leaking radiator cap or that the radiator itself has a leak. If you smell it inside your car instead, this might mean that your heater core has gone bad.[5]

Method 3
Making Your Car Smell Better

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    Get rid of other common smells in your car. If your car smells are unpleasant but aren’t a sign of mechanical malfunction, there are ways you can make your car smell better.
    • Try baking soda. This will remove odors from carpet. Maybe some food spilled on the carpet. Remove what you can, and then sprinkle baking soda on it. Rub it in. Leave it for a couple of hours, and then vacuum it up.[6]
    • Charcoal also absorbs smells. If you leave a chunk of grilling charcoal in the car for a couple of days, the charcoal will absorb a lot of the car smell.
    • You could also put vanilla or another scent on cotton balls, and leave them in your car. Or you could put a container of ground coffee in the car.
    • To deal with the smell of cigarettes, open your hood and spray air deodorizer in the intake valve. This is necessary because cigarette smoke also enters your car’s duct system.
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    Protect your car from growing smells. Use a little preventative maintenance so that bad smells don’t take over your car.
    • This can be as simple as vacuuming your car regularly to remove dirt that’s been tracked in it or food crumbs that have spilled.[7]
    • Don’t let trash accumulate in your car. Keep a small plastic bag in the car to immediately deposit trash inside, and throw it away every few days (or even every day).
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    Shampoo your car regularly. If you've got a problem with food or drink spills, it's a good idea to shampoo your car's floor mats or seats.
    • Remove floor mats, and shampoo them immediately if food spills on them. Just take detergent and water, and scrub them. You can also buy car upholstery shampoos in many auto stores.
    • It's a good idea to test the detergent on a small spot first. You can also use carpet cleaner, and a wet/dry shop vac. Just spray the carpet cleaner on the seats. Vacuum it up.[8]
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    Diagnose the odor as mildew. One of the most common odors in a car is mustiness. It can smell like old gym socks. Just hanging up an air freshener won't permanently eliminate the problem.[9]
    • If you smell this odor, especially when you turn on your heater or your air conditioner, it’s probably mildew that grew because moisture condensed inside your air conditioner.
    • The key is to dry out the air conditioning system. You can do this by turning off your air conditioner and running the fan on high for about a mile.
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    Remove other causes of car mildew. You’re not going to be able to camouflage this one with a bunch of air fresheners. You’ll have to get at the root of the problem, which is likely moisture or humidity inside the car.[10]
    • Look for condensation inside the car. Remove the floor mats to see if they appear wet. Look in the trunk and in the spare tire storage space. It’s also possible that the air conditioning filter is causing the musty smell. See if the floor mat is wet near the air conditioner.
    • If you smell the odor from the floor or trunk, remove all floor mats. If the smell is coming from the air conditioner, remove the filter in it. Just open up the front cover of the unit to remove the filter.
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    Get rid of the moisture that's causing the mildew. Take a rag, and wipe off any moisture that you can find. If you see any mildew or mold on the area, use a nylon scrub pad to remove it. Try not to scratch the car.
    • Now you will need to dry the area to remove the moisture causing the smell. You can use a hair dryer if the area is small enough or a wet vacuum for larger areas. You could use a cotton swab in the air conditioner.
    • You might want to apply anti-mildew solution to the area. Dry any of the floor mats you removed, and then put baking soda on them. Let them hang outside for 24 hours, vacuum, and put back in the car.[11]


  • See a professional if the smell is not going away before it gets worse and costs more in the end.
  • Don't smoke a cigarette while trying to diagnose gas smells.
  • Keep your car clean.

Article Info

Categories: Car Maintenance and Repair