it looks like Motors TV have terminated their contract to be included in the SKY EPG, therefore your Sky Box won't display the channel.
There's a very long discussion on the SKY help forum here
http://helpforum.sky.com/t5/Entertainme ... -p/2428453 it goes to over 11 pages and gets very boring, but hopefully you can fathom out what's happening.
There are instructions to add the channel manually, which means you can still watch it, but of course you won't be able to schedule SKY+ record.
I think it's going to be online only in the future, hope you have a good broadband link? Have a look at the website
https://www.motorstv.com