Red light Deere 6630 std

[beltbreaker]

Carting grain around and twice while pulling hard up a brae the red engine light and buzzer comes on. Ease throttle back and it goes off. Air filter is nearly new diesel filters changed 80 odd hours ago. Just over 5k hrs
Thoughts?

Cheers BB.

Ps I doubt it's the cylinder head

 

[M-J-G]

Water in the fuel filter, or a faulty sensor