Your serial number shows this unit was wholesaled by Honda on 8/8/2012, and unless you have proof-of-purchase, that would be the start date of the 36 month warranty. So either way, the mower is still under warranty. That said, the warranty covers defects, not wear, neglect, or lack-of-maintenance, so keep that in mind.
Might want to discuss with your local Honda dealer and let them evaluate the mower. It is possible any needed repairs might be covered under warranty. Be sure to confirm with the the dealer if warranty applies and what charges (if any) you'd be responsible for before authorizing any work. Beware, this is a very busy time for mower service departments, so the sooner you get it in the better.
FYI, your mower is a slip-belt design. As you turn the SmartDrive control, you are tightening the tension on the belt.
Now if you elect to DIY the repairs, here are a few things the shop manual suggests:
1. Adjust the SmartDrive cable.
2. Park the mower on flat, smooth surface. Engage SmartDrive and hold the mower from moving forward. Listen/watch for intermittent wheel spin / clicking. If you DO hear clicking/ratcheting, inspect the wheel drive ratchets and pinion gears for wear, damage, debris.
3. If the wheels stop, but you DON'T hear clicking or ratcheting noises, the transmission itself may have an non-servicable internal fault and require replacement.
Resources:
Find A Honda Dealer
Honda Power Equipment Shop Manuals on eBay
Honda Power Equipment Shop Manuals on Amazon
Honda Power Equipment, Engines and Marine Factory Parts Lookup
