Step 1. Make a new document 4 x 4 px. Select the colours and fill as shown below.



Step 2. Now that is done we can define the pattern. Go to Edit > Define pattern. Name as you wish then hit ok.



Step 3. Now you have made the pattern you can now select the area you wish to make carbon fibre and then go Edit > Fill > Pattern and select yours, hit ok again and VIOLA! You have carbon fibre.

Here is a basic example of the pattern in effect.