Where does the magnet go?

The sensor is so far away from anything metal for me to place the magnet, definitely farther than 5mm. I have the plastic wheel adjusted exactly 5 mm, all the around from the end of the roller bar. I keep getting error code 3 and it will not run longer than 7 seconds :(
Please post pics of where the magnet goes and how it should look, ya' know if anyone had their treadmill flipped over and the cover taken off.