How to Find the Source of a Bad Odor in a Car

Interior odors in cars can be caused by numerous things, each one requiring special attention. It is not possible to list all of them here, but these should be the most likely culprits and some advice on dealing with them.

Steps

1. 
   1
   Look for an obvious source. To rid a car from odor, determine the source by considering typical origins of odors. The most common is kids spilling food or beverages, and if this is obvious, get a can of carpet and upholstery cleaner and treat it according to label.
2. 
   2
   Do a little detective work. If the odor is a mildew-like musk, you may have a leaky floorboard, for instance a loose chassis drain plug allowing rain to splash inside. A wet car carpet will grow mildew and mold rapidly, especially with closed windows. Feel the carpet, especially the lower floor board sections where water might accumulate. When "damp spots" are located, apply a weak solution of chlorine bleach, not exceeding 2 oz per gallon. Then speed dry with either a wet/dry shop vac or airing out with windows down in the sun. With unexplained floor wet spots, crawl under the car and look for plugs missing and openings. These plugs are black rubber inserts, about 1.5"X 3", placed in lower parts of the car floor.
3. 
   3
   If you haven't found the odor source, check the glove compartment, ash receptacles, trunk, and beneath seats. Most back seats remove by lifting at the front edge and sliding forward. The force required to remove the seat varies and some cars may have threaded fasteners which would need removing.
4. 
   4
   Check the owner's manual to see if your car has a cabin air filter in the AC duct work. Since AC acts as a dehumidifier, this filter can dampen with condensation, becoming moldy, blowing odors into the car. By selecting 'return air' or 'recirculate' on the AC controls, less moisture enters the system, decreasing the water being removed at the evaporating coil, decreasing possibility of smelly mold. The filter is replaceable but complicated, so consult a professional in this instance.
5. 
   5
   Check the engine and exhaust system. It is not unusual for these to cause odors, but not normally detectable except when the car is idling or traveling at low speed. Gasoline odor is especially serious, and if you think you may have a fuel leak it should get immediate attention. Antifreeze has a unique, sickly-sweet odor, and a radiator leak will cause the engine temperature to rise, boil over and quit. Oil leaks, especially above the exhaust manifold where the dripping oil actually burns off, can smell, but at highway speed it will likely disperse to drivers behind you. An engine exhaust leak has very low odor potential, but if you suspect one, it can be the most serious of all. When the engine runs, these fumes can accumulate inside the car, becoming very toxic when concentrated. Mostly, significant exhaust leaks cause loud exhaust sounds.
6. 
   6
   Look under the car and around the tires. If you have not succeeded in finding the odor source, it could be road-kill under the chassis. You may notice this distinct odor at one of the quarter panels, and a car wash pressure washer, to thoroughly spray out the suspect area, could help. Do not spray water up into the engine compartment and knock wiring couplers, vacuum hoses and even spark plug wires loose.
7. 
   7
   Inspect behind the front grill for feathers of a bird stuck in the radiator.
8. 
   8
   Because types and sources of odors vary, this article doesn't cover remedies for the odor itself, concentrating on locating and removing it. A variety of commercial deodorizers and cleaning products help, also, an open a box of baking soda. Shoe "Odor Eaters" can be placed under seats, but unless you eliminate the odor source, anything is just a stop-gap solution.

Tips

• Choose an air freshener, something pleasant.
• Check the owner's manual for maintenance suggesting air conditioning duct work service, especially cabin air filters.
• Leave your windows down when possible to let the carpets and fabrics breathe, especially on low humidity and sunny days, and when driving in light traffic.
• Be aware of when the odor "peaks" or is most noticeable. As stated, exterior sources are more likely noticed when idling or driving slowly. Food and internal sources are most noticeable when the car is parked for a time with windows up.
• If unable to find the odor, pay a professional to give the interior a complete cleaning, including Scotch guarding the upholstery and carpet.
• Check the trunk often for misplaced clothes, especially sneakers and wet swimsuits, also fruit or other food items which can fall out of a grocery bag unnoticed.
• Use your nose to find the odor source. Or, get help, especially if it is particularly offensive.

Warnings

• Odors can be warnings of several imminent mechanical failures or worse. Gasoline odors, antifreeze, burning oil, wearing clutch and brake friction plates, and belt slipping odors can actually be life savers if they head off a breakdown on an expressway in heavy traffic. Don't ignore them!