Schnauzers naturally smell bad because they have oily skin, and regularly bathing them will help them to smell fresher. Sometimes, a bad smell from your dog is not just due to something being bad in their mouth, but it may also be due to diseases of their gums, infections of their bladders and/or kidneys, or even cancer.
If your Schnauzer smells bad, you need to find out where it comes from. Sometimes, it is as though some foul smell emanates from the whole body. However, it may be from just one source such as the nose or the ears. This will help you decide what to do to get rid of the smell.