Audi S4 Smell in the car Inspection at your home or office.

In-car smells can indicate minor or major mechanical issues, depending on the nature of the smell, its location, and whether any fluid leaks or other symptoms are present.

Typically, smells originate from a fluid leak or malfunctioning component.

• Fluid leaks: Fluid leaks are the most common source of unusual smells in a vehicle. Gasoline, oil, coolant, and other fluids can leak from ruptured hoses, lines, gaskets, and seals.

• Malfunctioning components: Many components can cause fluids to leak if they break or rupture, but some components themselves can cause unusual odors if they stop working properly. For example, an overcharged battery produces excess heat that results in the battery putting off a strong scent of sulfur (like rotten eggs).

Common car smells:

Smells emanating from under the hood or under the vehicle often take on a specific, recurring odor. If your car is putting off one of the following scents, take note of it -- it’s likely your issue is one of those commonly associated with that particular smell.

• Exhaust: Have the vehicle inspected as soon as possible. Carbon Monoxide (CO) is a major component of vehicle exhaust, and is often referred to as the “silent killer.” If exhaust fumes are present in the cabin, so is CO. CO can cause loss of consciousness, and prolonged exposure can cause death.

• Gasoline: On modern automobiles, fuel odors should not be detectable at anytime beyond refueling. A strong smell of gasoline can indicate a leaking fuel supply component (fuel filler hose, filter, or lines) or an evaporative emissions component (purge valve, hoses, or canister). Have the vehicle inspected by a professional immediately.

• Sweet (like maple syrup): When a sweet smell is detectable, the likely culprit is coolant. Coolant travels throughout the engine, radiator, various hoses, and the heater core, which is usually located under the dashboard. A coolant smell will usually be followed by an overheating condition, so a thorough visual inspection should be performed immediately. At no time should the radiator cap on a vehicle at operating temperature be removed, as hot coolant has the potential to cause serious injuries.

• Sulfur (like a struck match): The most likely cause of a strong scent like rotten eggs is a catalytic converter being overwhelmed or reaching failure, but it could also be the result of an overcharged battery or fuel system issue. To avoid costly repairs, have the car inspected as soon as possible.

• Burning wood or rubber: Overheating the brakes or tires can cause the car interior to smell of burnt rubber. A slipping or malfunctioning clutch can cause the interior to smell like burning wood. In both cases, letting the components cool off for a few minutes may solve the problem. If the smell persists, it may indicate a slipping clutch, or a brake component that is seized and in need of service.

• Hot oil: As engine oil leaks from a failed gasket or seal, it typically lands on hot components and gives off a distinct smell. Small amounts of oil may neither leave traces on the floor nor be easily seen without a thorough inspection. It’s important to address the smell of oil even if no oil is actually visible.

• Mildew or mold: Usually, a musty odor is indicative of buildup on the vehicle’s evaporator or a cabin air filter that is due for replacement (if the vehicle is so equipped). An inspection of the duct system will usually be required. If the vehicle has a cabin filter, a replacement may be necessary.