This error code does not appear often. However, it is easy to clear in most cases. It appears when a foreign object gets stuck in the door well. There are other codes indicating similar problems: HE and TL. In fact, there are several factors that can cause this error: excessive foaming, overloaded drum, and loose wiring.
Pusn the End of Cycle button and unplug the machine. Wait a few minutes and plug it back in. If the error appears again, address the issues mentioned above: switch to a less foamy detergent, do not load too much laundry, and check the wiring.