Hey guys, new to the site. A lot of informative info here, I've just solved that darn Brake & ABS light problem thanks to all the useful posts.

Anyways, my brother's 2000 Cummins auto transmission is coming up with a code P1693 DTC Detected in Companion JTEC Mod, now I see many of the people who have this problem also get another code after this is thrown. However, this is the only one which shows up.

The light is on constantly, and runs very very poorly on occasion. Not only that, but the tach. is intermittent. Sometimes it'll work, and other times it won't. I'm not sure if this is a seperate issue, but I'd like to figure out what is causing the code P1693.
Anyone have any ideas? I'm not at all familiar with these trucks. Thanks!