Quite possbily the EGR valve is sticking.

I had a company owned 2010 T.D V.W Transporter that would go to Limp with the engine management light on and reset with ignition off / on.
No codes stored.
It was B.T.Fleet maintained, it went in to the workshops several times, they couldn't get it to go to Limp but thought it would be EGR.
They suggested next time it happened to drive back to them without switching the engine off, which I did.
They plugged the scanner in and it showed the code for EGR fault.
Switched off /on and the code had disappeared.
New EGR fixed it.

As above post, the codes need reading while it's faulty and running.