Yes. To have an active CDL, you need a current DOT physical, always.
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Yes. Always.
No
-spacespace- No
If you don't have a valid DOT physical, your CDL is null and void. The only exemptions to CDL requirements are farm vehicles, military vehicles, emergency vehicles, and recreational vehicles, within the conditions specified for those exemptions.
When you go to the DMV to get your CDL, you'll be expected to show either your DOT medical card, or the DOT physical long form. Additionally, any employer hiring you as a CMV operator is going to require you to present your DOT physical card, and possibly the long form physical, as well.
Your license won't be suspended, but you'll be forced to downgrade. You can't hold a CDL if you can't pass a DOT physical. And if you can't pass a DOT physical, you have much bigger problems than your license to worry about.
You could teach classes pertaining to the written tests, but you couldn't teach the on-road portion or any other portion of the training which involved actually operating the vehicle. CDL students on a permit must be supervised by a fully licensed CDL driver, and you can't even be in actual physical control of a CMV without a CDL.
Commercial driver's license can be obtained from the Department of Transportation. All you have to do is appear in their office personally and pass the physical exam, drug test, and the CDL test.
It's a condition which disqualifies you from passing the mandatory DOT physical.
You won't be able to pass a DOT physical, and will lose your CDL.