fault with auto focus

[toon man]

can someone help me please. after a days shooting at the sunderland airshow my canon 30d with 100-400 L lens failed to auto focus the lens was trying but failing to reach full focus.
not long ago i had a problem with my genric battery grip i am living in hope that this can cause the same problem

 

[Martyn...]

Remove the grip to rule out that causing the issue.

Sometimes it can be the contacts, they either get a bit dirty or fail to make proper connection, quite common with bigger lenses, try removing and re-seating the lens.