A reduced cube with the last layer oriented and the corners in their correct positions.
Hold the cube with yellow facing up. The repair swaps the top-front (UF) and top-back (UB) edge groups.
1. Recognise two swapped edge groups
On a correctly reduced 4×4, exactly two complete edge groups can remain swapped even when the corners are in their correct positions. This is PLL parity, which affects edge positions. It differs from a flipped edge group and from a standard cycle involving three edge groups.
Put the corners in their correct positions first. Corners in the wrong 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 needed, practise those layer widths 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.
- Two opposite groups swapped: rotate the whole cube sideways so the groups are at the front and back of the top layer, then apply the repair.
- Two adjacent groups swapped: keep yellow facing up and use any side as the front when you apply the repair. The two swaps leave a standard 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 is still paired and each centre is a single colour. If three top edge groups are still out of place, finish with the standard three-edge cycle. Apply the parity repair only once for this case.
A 4×4 solve can have OLL parity, PLL parity, both or neither. Apply each algorithm only if its case appears. The final lesson helps you choose the right steps when solving 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 when you look directly at that face. A prime mark (′) reverses the turn. A 2 means 180°. Keep the same face at the front throughout an 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 going through the moves one at a time. The prepared example shows a specific action. Use the lesson’s setup instructions to recognise when to apply it to your own scramble.
Watch one worked example
UF and UB are swapped on this prepared cube. For 2R2, turn a single inner layer. For Uw2, turn the top two layers together. Use the correct layer width for each move.
Starting grip. Yellow up · blue at the front · red on the right. Follow any written instructions for rotating the whole cube.
0 / 7
Loading 3D cube…
Prepared position · 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 focus.
Copy this exact example on your own cube
Start with a solved 4×4, yellow up and blue front. Apply the setup below from left to right. This creates the example’s starting position. Keep this separate from the ongoing scramble you are solving through the course.
U2 Uw2 2R2 Uw2 2R2 U2 2R2Then follow the lesson sequence. If your cube’s colour scheme differs, match the piece relationships using your own colours.
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 edge groups are opposite or adjacent. Set up the cube for your case and apply the repair, then check the corners and edges again before finishing.
Open a 4×4 Digital Cube for practiceOpens in a new tab so you can refer to this lesson while you practise. Check for yourself whether you’ve met the lesson goal. The Digital Cube does not grade your work.
If you get stuck
I used the repair, and now three edge groups are out of place.
This is expected if the two edge groups that were originally swapped were adjacent. Finish with the standard three-edge cycle, holding the solved side at the back.
The centres are mixed after the sequence.
Check that you turned only the second layer from the right for 2R2 and the top two layers together for Uw2. Complete all seven moves.
Before moving on
Check your result
Your cube at this stage
Two-edge swap corrected
The edge groups and centres are intact. A standard three-edge cycle may remain, as it does in this example. Finish it using 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.