Tying up a pinned opponent

[Trebonius]

Do you need to make a grapple check to tie up someone who is pinned?

Background - bar room brawl - no one has armour or weapons.

2 party members onto the BBNG.

Round 1 - partner successfully grapples our opponent. I move in and join the grapple (aid another)

BBNG tries to break free - and fails

Round 2 - partner is on a roll and converts grapple into a pin - excellent!

My action - I want to tie our opponent up.

The following is an action if your opponent is grappled.
Tie Up: If you have your target pinned, otherwise restrained, or unconscious, you can use rope to tie him up. If you are grappling the target, you can attempt to tie him up in ropes, but doing so requires a combat maneuver check at a –10 penalty. If the DC to escape from these bindings is higher than 20 + the target's CMB, the target cannot escape from the bonds, even with a natural 20 on the check.

The question is do I as an additional character have to make a grapple check and if so with what modifiers?

[Carbon D. Metric]

No you don't have to do that, you are making a simple aid another action to add +2 to the roll of the person doing the tying etc.

[BltzKrg242]

You seem to have left out a good deal of the Tie Up section:

Tie up:

Tie Up: If you have your target pinned, otherwise restrained, or unconscious, you can use rope to tie him up. This works like a pin effect, but the DC to escape the bonds is equal to 20 + your Combat Maneuver Bonus (instead of your CMD). The ropes do not need to make a check every round to maintain the pin. If you are grappling the target, you can attempt to tie him up in ropes, but doing so requires a combat maneuver check at a –10 penalty. If the DC to escape from these bindings is higher than 20 + the target's CMB, the target cannot escape from the bonds, even with a natural 20 on the check.

The target is most definitely "otherwise restrained" if he is pinned so you can do as a standard action and he has to beat your CMB +20 to get out afterwards.

[Quantum Steve]

You only have to make a grapple check if you're the one pinning the target.

Tying up an opponent you partner has pinned is no different than tying up a helpless opponent. You simply do it, no roll required.