A reduced cube with last-layer orientation complete and corners positioned.
Yellow up. The repair exchanges top-front (UF) and top-back (UB) groups.
1. Recognise two exchanged groups
On a correctly reduced 4×4, exactly two complete edge groups can remain swapped while corners are correctly placed. This is PLL parity, a positioning exception. It differs from a flipped group and from three edges that simply need a normal cycle.
If you have not positioned the corners, finish that stage first. Mixed corner positions can make the edge problem difficult to diagnose.
2. Read the inner-layer move carefully
2R2 means turn only the second layer from the right by 180°. It does not mean R2 or Rw2. Uw2 turns the top two layers together by 180°.
If you need to, practise turning the correct layers in the notation lesson before trying the full repair.
3. Apply the opposite-edge repair
2R2 U2 2R2 Uw2 2R2 Uw2 U2
This exchanges the UF and UB edge groups while restoring centres and preserving the corners.
- If two opposite groups have swapped places, rotate the whole cube sideways until they are at the front and back of the top layer, then apply the repair.
- If two adjacent groups have swapped places, hold yellow up and apply the repair with any face at the front. The combined swaps leave an ordinary three-edge cycle. Put the solved side at the back and use the final-edge cycle once or twice.
Complete all seven moves before checking the result.
4. Finish and inspect
Check that every edge remains paired and the centres are solid. If three top groups remain out of place, solve that ordinary cycle; do not keep repeating parity.
A single 4×4 solve can involve OLL parity, PLL parity, both or neither. Apply each algorithm only if its case occurs. The final lesson helps you decide which steps to take from a fresh scramble.
Need a reminder of the move notation?
R right · L left · U top · D bottom · F front · B back. A letter on its own means a 90° clockwise turn as you look directly at that face. An apostrophe (′) reverses the direction. A 2 means a 180° turn. Keep the same face at the front throughout the algorithm.
Rw turns the rightmost two layers together. 2R turns only the second layer from the right. 3Rw turns three layers. x rotates the whole cube like R, so the old front becomes the new top.
Watch, then try
Work through an example
Start by stepping through one move at a time. This prepared example shows a specific action. Use the lesson’s setup instructions to recognise when to use it on your own scramble.
Watch one worked example
In this prepared position, the UF and UB edge groups have swapped places. Turn a single inner layer for each 2R2 move and the top two layers for each Uw2 move. Both layer widths are essential.
Example grip: Start with yellow on top, blue at the front and red on the right. Follow any written instructions for rotating the whole cube.
0 / 7
Loading 3D cube…
Starting position set · 0 / 7 moves
Use Next move to follow the sequence.
Drag to inspect other faces. Use the arrow keys to rotate the view when the cube has keyboard focus.
Copy this exact example on your own cube
Start with a solved 4×4, with yellow up and blue at the front. Apply the setup below from left to right to create the example’s starting position. Keep this example separate from the scramble you’re solving throughout the course.
U2 Uw2 2R2 Uw2 2R2 U2 2R2Then follow the lesson sequence. If your cube has a different colour scheme, use the relationships between your own colours to identify the equivalent pieces.
Compare the starting position and the result
Drag each cube to inspect its other faces.
Explain it to yourself
Check your understanding
Now use your own cube
Your turn
Check whether the two misplaced groups are opposite or adjacent. Set up the cube for your case and apply the repair. Check the corners and edges again before finishing.
Open a 4×4 Digital Cube for practiceOpens in a new tab so you can keep this lesson open while you practise. Check for yourself whether you’ve met the lesson goal. The Digital Cube doesn’t assess your result.
If you get stuck
I used the repair and now three edges are out of place.
If the original swap involved adjacent edge groups, this is expected. Finish with the ordinary three-edge cycle, keeping the solved side at the back.
The centres are mixed after the sequence.
Check that 2R2 turned only the second layer from the right and that Uw2 turned the top two layers. Make sure you complete all seven moves.
Before moving on
Check your result
Your cube at this stage
The two-edge swap is fixed
All edge groups and centres are intact. An ordinary three-edge cycle may remain, as it does here. Finish it with the 3×3 method.
Confirm these on your cube. Watching the animation alone does not complete the lesson.
Tick each item once you can do it yourself.