I've seen this reported a few times on the forum and two fixes have been reported: clean the Z-axis mechanism and replace the cable (7-pin?) between the adapter board and the motherboard. I'd like to know if anyone has more details and success stories.

The blue LED did go on and off when the lead screw was rotated manually. After this bit of manipulation, the P2 did start up a couple of times and then had the same error. I didn't see any dirt or debis on the parts.

We replaced the Z-axis adapter board, which involved re-doing the connectors and checking them. The error was still reported, and the blue LED still operates as expected.

xTools's next suggestion is to replace the 7-pin cable in the drag chains, which would require a lot of work. Is it possible to expose the motherboard and connect the cable, temporarily, outside of the drag chains for testing?

I'm going to have a serious go at cleaning the parts. What lubricant is best? I like 3-in-1 “dry” lock lubricant but if there is an official recommendation I'll use it. ( I've asked the chat function but it hasn't responded yet.)