450 Fortwo 600cc & 700cc

The problem selecting reverse on the original smart fortwo was usually due to a faulty brake light switch. 
Remove the brake light switch and test it to ensure it's doing what it should.

452 Roadster 700cc

The problem selecting reverse on the Roadster was usually due to a faulty brake light switch.
Remove the brake light switch and test it to ensure it's doing what it should.

451 Fortwo 999cc

When the 451 fortwo started exhibiting the same problems when selecting reverse, people immediately assumed that smart hadn't learned their lesson and that a faulty brake light switch was to blame as with the previous models.

Unfortunately this just wasn't so. As yet I have heard no reports of the brake light switch failing.

The fault is no down to a faulty clutch but thankfully smart have been known to change the clutch under warranty. If you are out of warranty then there seems to be a way to get around the problem.

When you stop, hold the foot brake and select reverse, if it just flashes an N at you on the speedo LCD instead of selecting reverse, try this. Reselect 1st gear, drive forwards a few inches and try selecting reverse again. So far I have had the problem appear about 5 times and on each time, this quick method allows you to select reverse.

I can't quite decide if it's a physical fault with the clutch or some kind of alignment or sensor issue.