Mold or mildew odors in a car can be a challenge for the average owner of an older car. As a professional detailer, you can often solve this problem or at least provide helpful insight to a customer who is suffering from this issue if you know the primary problem areas that can cause it.

Sometimes, the problem cannot be easily solved. Being transparent with the customer about this is important to maintaining a good relationship and earning his or her trust. You also need to ensure that your business is profitable. Chasing down an elusive and difficult-to-solve problem can put you in the position of either having to charge too much for your work or eating up a good bit of labor time.

Related: How to treat auto malodors

As the expert, you do not want to tell your customer that you do not know what to do about it or that it is not worth your time. Word of mouth is often the biggest source of business, and you want to leave all of your customers feeling like you know what you are talking about and that they at least gained some valuable insight, even if their problem was not solved by you.

What causes these odors

Moisture is almost always the culprit in some way — typically, water collecting inside the vehicle somewhere. The water may be from rain or snow gaining access through a failed seal. It could be possible that the water is generated inside by the vehicle itself as condensation from the cooling system.

Another possibility is simply water being tracked into the vehicle due to the circumstances of the driver using the car, such as snow on boots.

It is also possible that something left under the seat or rodents nesting in the car and having died are causing the smell. If this is the case, the problem will likely be new as opposed to a long-standing problem, and this may be a helpful indicator of where to start your search for the source of the problem.

Identifying the source of the smell

It is important to try to determine where the smell is originating from. If you are going to solve the problem, you need to tackle the problem head-on. Simply throwing fragrances at the smell is not going to prove to be a long-lasting solution.

If the problem is from a failed seal in a window, as an example, the problem is not likely to go away anytime soon, unless you happen to live in the desert. It can be difficult or impossible to identify the source.

It is important to communicate to your customer that this could be the case, and not knowing where to start will make solving the problem very difficult. If you can identify the source of the odor, such as from the dashboard vents or damp carpet in the driver’s footwell, you will be far better able to succeed.

Cabin filter

A frequent source of odors coming from air vents in a car is an old cabin filter. Although as a detailer you may not have access to a new cabin filter for that specific vehicle in question, you can pass along the advice of replacing this filter, which is typically quite inexpensive, as an easy step to take that should be done as part of regular maintenance anyhow.

It is also worth inspecting the area around the cabin filter to ensure no rodents have nested or died in the area or that no water is collecting there.

Related: How to change out an air filter

Heater core

An old heater core can often be the source of mold or mildew smells coming from air vents. Replacing a heater core can be an expensive option in many cars and may not be worth it to the customer to attempt.

Sometimes, a heater core can be disinfected by spraying a trusted disinfectant product in the air intake after removing the cabin filter and following the manufacturer’s use guidelines. Also, running an ozone machine inside the car with the air set to recirculate can help disinfect the core.

Inspect under seats

Lots of things fall onto the floorboard and find their way into unreachable locations under the seats of a car. Some of these things do not end up smelling too good after some time. Doing a thorough sweep under the seats is always a good option.

It may be worth removing the seats to completely inspect the area. In addition to looking for anything organic that could be decaying down there, you will want to inspect for wet areas. Water leaks can occur in a distant part of a car or truck, but customers end up having water pool under the seats if it happens to be the lowest point in the cabin.

Inspect the footwells

Carpet can get funky smelling for many reasons, including water leaks, clogged AC drain lines, drink spills, dropped food that has been ground in or something else. A thorough carpet cleaning could be a default service that is suggested even if no source of the smell has been found.

The carpet could be the source of the odor itself or could be harboring some of the smell that is emanating from a different part of the vehicle. Be sure to include the floor mats in your service, even if they are not carpeted.

Inspect the seats

Checking the seats is important. If the seats are leather or vinyl, they are less likely to be the source, but liquids and smells can penetrate and collect in the foam. There will likely be an accompanying stain to help you locate a problem.

Also, crevices where cushions meet could be holding something nefarious that needs to be removed.

If the seats are fabric, it may be wise to thoroughly clean them for the same reason you would want to clean the carpet. There may be smells trapped within them that a good cleaning could remove and help cut down on the problem.

Inspect the trunk and other storage areas

Leaks, dead animals and other sources of foul odors could be hiding in these areas and working their way into the cabin of the car. Thoroughly inspect all of these areas for signs of moisture, discoloration or smells. They too may need to be cleaned if an odor is found in these areas.

Limits and opportunities

If you find discoloration somewhere along the headliner, you may find the source of a leak from a sunroof or other opening in the roof. Finding stains on the headliner is good news, since it significantly narrows down the hunt for a leak. Drain lines around sunroofs often get clogged over time and allow water to back up and leak into the cabin.

Also, sunroof seals get brittle with age and eventually fail. You may find that the smell is coming from the headliner itself. There is usually some fabric or foam there that can absorb water, and it could be the source of the mold smell. Before attempting to clean the headliner though, you should suggest the customer attempt to have the leak resolved first.

A list of things that you should recommend having checked by a mechanic as sources of moisture or odors are the cabin filter, heater core, clogged AC drain lines, clogged sunroof drain lines, worn window seals or convertible top weather stripping.

Things you can do are thoroughly inspect the interior of the car, including the trunk and other storage spaces. You can also offer to shampoo the carpets, mats, fabric seats and headliner. You can wipe down all surfaces to remove any surface contaminants that could potentially be a source of the smell. You can also attempt to neutralize the mold or mildew with an ozone machine. You may not be able to solve the problem for the customer, but you can help him or her.

Not all of the solutions to mold and mildew smells should be tackled by a detailer. Some should be handled by a trained mechanic. By knowing what the sources of the problem are and how to identify them, you can properly consult your client and at a minimum leave your customer well informed with you looking like an expert instead of someone who would not or could not solve the problem.


Will Creech is an auto enthusiast that has been obsessed with cars since long before he could drive. He maintains the auto detailing blog DetailDIY.com.