John Deere skidsteer 317 starting problem

[WalterBloom]

I bought a new John Deere 317 around 16 months ago and have done just 92 hours in total. I did some work recently and the following day the machine started perfectly but shut down after about 5 seconds. There are no diagnostic codes coming up, I have changed the main airfilter, fuel filter and in-line fuel filter, and I have checked that the safety belt light goes off when I click the safety belt into place. I have tried to start the machine many times since but with the same result. The timing out is always exactly the same (just under 5 seconds) which suggests that this is a safety feature time-out rather than a 'varying' problem. I have tried the local John Deere agent without much success but I plan to see their workshop manager in person if I can. I hope that there is an easy solution!