This step goes over the remaining 2 parity error cases (*There are really 3 more, but we basically skip the corners parity error when using my Step 6 algorithm) that you may see when solving the 4x4 and also shows how to solve the 4x4 as a 3x3 cube thus allowing you to finish solving the cube completely!
**IMPORTANT** FOR MOST OF THE 3X3 ALGORITHMS, THERE ARE CERTAIN WAYS YOU MUST POSITION THE CUBE BEFORE YOU PERFORM THE ALGORITHM. I DO NOT GO INTO DETAIL ON HOW TO PERFORM THESE MOVES AND SO HAVE INCLUDED THE STEPS IN THE 3X3 TUTORIAL WHICH CORRESPOND TO THESE MOVES. PLEASE SEE MY 3X3 TUTORIAL FOR MORE DETAILS IF YOU ARE HAVING DIFFICULTY USING MY ALGORITHMS. THANK YOU!
*NOTE* If you do NOT use my 3x3 method to solve the 4x4, you may come across a FOURTH parity error. This error affects the position and/or orientation of the top CORNER pieces. ALL YOU HAVE TO DO is use the algorithm I have listed below and also demonstrated in THIS tutorial...the one that corresponds to STEP 6 of my 3x3 tutorial. That algorithm to CORRECT CORNER PARITY is
R' F R' B2 R F' R' B2 R2
That will CORRECT any CORNER parity case you may have. If you are UNSURE of how to use that algorithm exactly, please see my step 6 of my 3x3 tutorial.
Algorithms (IN ORDER):
Interchanging the two parity cases you see before finishing the top face (from step 4 of 3x3 tutorial). *If you have the 2x3 block, you want to hold it horizontally so that the 2x3 is all the way to the LEFT on the TOP face (see video*)- Orienting Last Layer (OLL)
F U R U' R' F'
Flipping over the top edge piece (the second PARITY case we see)*Hold the flipped edge pair on the FRONT face in the TOP middle edge pair position (see video*)- Orienting the Last Layer (OLL) - **ONLY SEEN IN 4X4 and also 5x5 cubes**
(Rr)2 B2 U2 (Ll) U2 (Rr)' U2 (Rr) U2 F2 (Rr) F2 (Ll)' B2 (Rr)2
Finishing the top face (3x3 tutorial step 5)- Orienting the Last Layer (OLL)
R U R' U R U2 R'
Positioning Top Corners (3x3 tutorial step 6)- Permuting Last Layer (PLL)***IMPORTANT NOTE*** THIS MOVE ALSO CORRECTS ANY CORNER PARITY ERROR YOU HAVE. If you are unsure of exactly how to use it, please see my step 6 of my 3x3 tutorial. You basically just have to find two corners which have the same color on the same face and set that face as your BACK** If you don't have two corners next to each other that have the same color, then ANY face can be the BACK****
R' F R' B2 R F' R' B2 R2
Last PARITY Case (flipping two opposite top layer edge pairs) - Permuting Last Layer (PLL)- **ONLY SEEN IN 4X4 ALSO**
r2 U2 r2 (Uu)2 r2 (Uu)2 U2
Allan (Fixing the top layer edges - might not need to perform this move, 3x3 tutorial step 7)- Permuting Last Layer (PLL)
L2 U' B F' L2 B' F U' L2