The most common source of bad smell and odour in your vehicle is the air conditioning system. This is because it is a small enclosed space that is constantly wet and moist. This gives rise to formation of mould, bacteria and fungus especially around the condenser and evaporator of the air conditioning unit. Apart from this, bad smell can also come from heated up rubber and plastic in the unit though this will be only when the AC is on for quite some time.
The cause of the smell is fungus, mold, and/or bacteria living in your vehicle’s climate control system (typically they congregate in the evaporator core and/or near the condenser in your A/C unit). These critters move into these areas because it’s a moist enclosed space, and while some cars have a bigger problem with this than others (some models are notorious for this problem), it’s very common.
There are a few things you can do to eliminate the problem.
1. Starting now, turn off the A/C at least 2 minutes before you shut off your vehicle – preferably 5 minutes – but leave the fan on. Just get in the habit of shutting your A/C off at a certain point on your commute. This way, your system will dry quite a bit before you shut off.
2. Buy a bottle of lysol antiseptic spray. Start your car, turn on the A/C system full blast, and make sure it’s set to pull air from the outside (the recirculate button should be off). Finally, roll down all the windows. Then, start spraying the lysol into the exterior air vents between your hood and your windshield. I’d spray for 20-30 seconds, wait a minute, then repeat until about 10 minutes have gone by. Then I would let the air conditioner run with the windows down for at least another 10 minutes before shutting down.
3. If step #2 doesn’t work (and it won’t always work), your dealership can try a foaming system cleaner sold by BG products. While some people say that this stuff is no better than lysol, I have seen it work when lysol didn’t.
4. Worst case, you can ask your dealer to remove the smell by replacing the evaporator core, condenser, drain pan, etc. However, this is rarely necessary as steps 2 and 3 usually take care of the problem.
Having said all of this, step #1 is key. if you don’t start shutting the A/C off (but leaving the fan on) a couple of minutes before you park your car, the mold, fungus, and/or bacteria will just come back stronger than ever.