Start with a reduced cube whose last-layer pieces are oriented and whose corners are in the correct positions.
Yellow up. The repair exchanges top-front (UF) and top-back (UB) groups.
1. Recognize two swapped edge groups
On a correctly reduced 4×4, exactly two complete edge groups can remain swapped even when the corners are in the correct positions. This is PLL parity, which affects edge positions. A flipped edge group and an ordinary three-edge cycle are separate cases.
Finish placing the corners before checking for this case. Corners that are still out of place can make it harder to diagnose the edge problem.
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 a refresher, practise turning the correct layers in the notation lesson before attempting 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 edge groups swapped. Rotate the whole cube sideways until the two groups are at the top-front and top-back positions, then apply the repair.
- Two adjacent edge groups swapped. Hold yellow up and apply the repair with any side facing front. Together, the two swaps leave an ordinary three-edge cycle. Find the solved side, hold it at the back, and apply 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 solid block. If three top edge groups are still out of place, finish with the ordinary three-edge cycle. Save the parity repair for its own case.
A 4×4 solve can involve OLL parity, PLL parity, both, or neither. Apply each algorithm only when its case appears. The final lesson helps you choose the right steps when solving from a fresh scramble.
Need a reminder of the move notation?
R right · L left · U top · D bottom · F front · B back. A plain letter 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 toward you 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 going through the example one move at a time. It shows a specific action from a prepared position. Use the lesson’s setup instructions to recognize when that action applies to your own scramble.
Watch one worked example
The UF and UB edge groups are swapped in this example. Use only one inner layer for each 2R2 move and both top layers for each Uw2 move. Both layer counts matter.
Example grip: yellow up · blue front · red right at the start. Follow any written whole-cube rotations.
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, with yellow on top and blue at the front. Apply the setup below from left to right to create the example’s starting position. Keep this practice setup separate from the scramble you’re solving throughout 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 recheck the corners and edges before finishing the solve.
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 grade your work.
If you get stuck
I applied the repair, and now three edges are out of place.
This is expected if the two swapped groups were adjacent. Hold the solved side at the back and finish with the ordinary three-edge cycle.
The centres are mixed after the sequence.
Check that you used only the second layer from the right for 2R2 and both top layers for Uw2. Complete all seven moves.
Before moving on
Check your result
Your cube at this stage
Two-edge swap corrected
All edge groups and centres are intact. An ordinary three-edge cycle may remain, as shown here. Use the 3×3 method to finish it.
Confirm these on your cube. Watching the animation alone does not complete the lesson.
Check off each item once you can do it yourself.