if your vehicle has air conditioning the smell could be caused by build up of bacteria on the heater matrix and in the vents, as this bacteria decays it causes a smell inside the cabin, this can be resolved by purchasing air specialist air con cleaner the is sprayed into the sir vents. the smell can also be caused by the heating of leaking coolant from the heater matrix, this would also combined with the car steaming up, check the coolant level to see if it has dropped.
Ventilation filter: 1 - Behind glove compartment 2 - Behind lower instrument panel. 3 - It's clipped in. 4 - Remove lower filter, slide down upper filter, remove ventilation air filter. 6 - Replace and put clip back on.
Bad heater core.
There are heater doors on the heat blower box that direct the path of the heat. Apparently the heater door to the floor vents is stuck closed.
The heater core has failed.
Is it a fish smell or a rotten egg smell ? FISH SMELL COULD BE A BAD HEATER CORE, THIS WOULD CAUSE YOU NOT TO HAVE HEAT IN THE CAR , BUT IT MIGHT NOT CAUSE CHECK ENGINE LIGHT TO COME ON UNLESS MAYBE CAR IS LOW ON COOLANT. ( THERE MIGHT BE A LOW COOLANT SENSOR TO TRIGGER CHECK ENGINE LIGHT) ROTTEN EGG SMELL COULD BE A CLOGGED CATALYTIC CONVERTER , WHICH WOULD CAUSE THE OXYGEN SENSOR TO TRIGGER THE CHECK ENGINE LIGHT, BUT IT WOULDN'T CAUSE THE LOSS OF HEAT.
Could be that your heater core is leaking May also have a plugged evaporator hole.
Fuel Leak. Possibly the Fuel Pump. Get it checked immediately.
The possible explanation for the smell may be that the heater core in the vehicle has a slight leak, therefore the smell of evaporating antifreeze will come through the vents until it is all dried up. Solution is to take the car to a garage and get the heater core replaced.
I just had that problem with my 99 Monte Carlo. When I accelerated or went uphill No air would come out of the dash vents. Problem was a Vacuum hose. Cost about $40 to fix.
The smell is not dangerous - however, if there is still a smell, there could still be urine, which could cause diseases and infections if you come in contact with it.
Check the Heater Core? Did it smell like oil or antifreeze. My Heater Core went, started blowing out smoke from the vent. Most Likely the Problem. "smoke" poured into my 1991 when the ac blew out all the freon and froze up the outside temp gage.
Yes, gnats can come out of dirty air vents. Gnats can actually come from anywhere. They are very pesky creatures.
If that smoke is more like steam, you have a leaky heater core.