Information from the web. Maybe this will help.
Smells come from one basic thing...moisture. Moisture creates mold and mildew. Spilled mustard is wet and, if it could only totally dry, it wouldn't smell, but there is always some humidity in the air, and that is why the smell keeps coming back.
That is why you don't use lots of water on an interior. A bad smell like pet urine soaks into your carpet. If you use hot soapy water on it, you dilute the problem, but spread it over a larger area. Once the smell is bad, then it coats everything inside the interior. The dash, seats, carpet, (and here is where you have to think like a smell) even under the seats, dash and on the headliner! Yes, that smell may be coming from above your head!
You must also determine how deep the smell is. Smells on the headliner will be surface only unless it has gotten wet somehow. But smells on a carpet can be down past the padding underneath. If the smell producing problem is on the surface, don't make it worse by soaking the entire area and spreading to deeper and wider. Use your capet cleaner in a small area and if the smell is deep, soak only that area with something to kill mold/mildew and neutralize smells. The stain from most spills is just nap deep, the smells can be much deeper.
DC CarCare has a product that can get deep into carpets/seats etc and get rid of smells. It's called Odor Wand. This product has almost no smell of it's own and can kill bad odors on contact...they won't come back.
SUPER TIP: To really make your car smell fresh, continue thinking like a smell and don't forget to deodorize the heat/vent/air conditioning (HVAC) system. Spray Odor wand in the air intake with your system fan on high and cycle it through the differnt modes. Mold/mildew can get into these area's and cause a bad smell every time you turn on the system.