What to do? "Unknown Diagnostic" code with Series 60 Detroit Diesels.

Time to bump this question again.

Hey av8tor69r !!
You fixed yet?? What was the bug??

Lucas Electric, the British Leyland Pyrotechnics company. If a wire connects to it, they can make it fry.
AC Delco would be the U S comparison.

My Perkins experience goes back years.
It is truly amazing anything worked at all, worked with crispy fried connects and in English Fashion,, was fixed with a shillelagh tap or two.
Undersized wires, mixed metal connects and a pile-o-spaghetti wire harness.

Also, re-read post #16.

There are still tens of thousands of old British cars on the road…

my first encountered with infamous green Lucas part boxes was in the early 80s but part for my mini moke …. later on in life first thing I did after buying my E-type was delucasify it by installing MSD ignition, delco rely alternator and modern gear reduction starter

Yep, An unknown diagnostic error.
The Penski team just programed for simple engine errors & stats.
Environmental (bad connects, low supply voltage, foreign equipment dropping and the Moon & Mars not aligned) issues were not coded.