I bought one of this - http://www.ebay.com/itm/251469018598 for my wife's car almost 2 years ago. It's exactly the same as in the first post with all bells... Works like a charm.
Not sure if it's going to work on your model. I used this for my CX-7. You can try though.
1. Car off, all belts unbuckled, parking brake on
2. Turn key to on position. you will see seat belt warning light light up red
3. After 1 min you must buckle and then unbuckle seat belt you want to...
The dealer should replace it for free for you if you just bought it. You have at least 90 days for a used car. Also why did you buy it in the first place if the Nav screen wasn't working?