Had a Nissan L02 with code 31 and some others because I unplugged mass air sensor and throttle pot. After I fixed the problem (plug on throttle body) came back week later all codes were cleared. My guess is that when truck goes through so many cycles of no fault all memory gets overwritten to 0. I could not get through peddal dance with this one no matter what I did. Throttle pot must be bit off. I have 4 komatsu units and I can do it on first time on them.