How do I fix self propelling mechanism?

Take a good look at the wheel assembly. Is it rusted on from being left exposed to the elements? Remove the cover for the self propelled mechanism. Is the drive belt intact? Try turning the small pulley.

These are very expensive units, a little overpriced. If the self propelling system isn't working, see if the cable is actually disengaging the self propelling clutch, if it is and there is still no movement, the trans is shot and the way you fix that unfortunately is to buy a new transmission gear box. Save money and do it yourself if your kinda handy.... Go onto you tube, search for self propelling transmission replacement and you will have a few to choose from. If you are going to take it to a shop, be prepared to pass out when they give you the estimate for the parts and labor. Maybe you will get lucky and it's just the cable which is a very easy fix and the cable shouldn't run ya more than 20 to.25 bucks. BUT get a Toro part no aftermarket! !

is the blade loose?is the pulley key way sheared as well as the key on the flywheel

You've not provided much information, but my guess is that you need a new belt. If this is not the issue, then please elaborate. Best of luck to you.

Toro 20016 self propelled walk behind when the wheels are engaged it moves, when the wheels are not engaged, the wheels look up.
What should I do to fix the problem

Yes it can be fixed. Try some basics first.
1) Check under belt drive cover for excess debris
2) Belt and Idler pulley condition
3) Control cable operation
a) rusted, frozen, broken, disconnected

I’m happy to assist further over the phone at https://www.6ya.com/expert/rolandw_c013176d62ee17ae

Take a look at your owners manual. It should have a parts diagram in it. With the manual in hand take a good look at the self propel assembly. Make sure every thing is there. It could be a spring came off, or belt broke. You might have to take off some covers to check. If you are somewhat mechanically inclined it shouldn't be a problem. I suggest taking a photo with a digital camera to make sure you get everything back the way it should be. Also in your manual it might have a troubleshooting page.

Good luck. Let me know if this helps.

roundo4

Your self-propel is probably belt driven. Belts can make an awfully lot of noise when unhappy. Possible it has rolled over and is running on the wrong side of the belt or is worn and just needs replaced. Hope this helps.,

remove plastic cover to access drive mechanism
check belt and remove debris and try again