Get a code reader on it, but mine did something similar, at least on startup. If you gave the glow plugs chance to think, it went into limp mode immediately. Just turning it over quickly and it didn't seem to notice.
As the 1.6 TDI (mine) uses the plugs for DPF regeneration however, mine had a habit of coming back on after a few miles driving. New glow plugs in the end sorted it.
Code reader will tell you for certain though. I used a bluetooth one and an android phone.