Ok thanks!
I think my controller might be the issue.
Putting your Sprinter details in a 'signature' that appears in each post you make would be of great assistance to anyone reading your posts and might make diagnosis/solution of the problem more accurate.
Also, since this problem is a 'chassis' problem, not a 'house' problem, it would have been better to post this thread in the NCV3 (guessing here) Sprinter section of the Forum or the general Sprinter section.
For example, the original GP module on early NCV3 Sprinters is a known point of failure and has been replaced with the 'latest & greatest' version. The GP module is trivial to access and replace for almost any DIYer, so all you would have to do is buy it and replace it yourself, for less than $400.