Id say replace the pins on MPU J4 with new ones, and maybe check the pins in the J4 connector in the wiring harness as well. As strangeways said, you can sandpaper the pins to see if that fixes the problem, but its really only a short term fix. replacing them is the best way to go for long term reliability. Thats what id be doing if it was my MPU board.
Cheers... Mitch
