obd2 not communicating

What size engine does your truck have? Being that it's a 1999 model, and what kind of adapter are you trying to use? Most likely you're trying to communicate with the CANBUS network? If you have a scan tool that is not communicating, I would check that you have power on pin 16 (12 volts) and Ground on 4 and 5. Another thing to look for is, does the check engine light come on when you turn the key to the "on" position. If it doesn't that means the engine computer is not powering up.

https://www.2carpros.com/articles/can-scan-controller-area-network-easy

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

Thanks for the reply.
It has a 5.9 Cummins, il6.
Supposedly it is not a CAN bus, it has the j1850 6 pin round plug. I bought a Y adapter, 6 and 9 pin to standard 16 pin. I do get voltage on data high and lo with engine running and can read them on pins 2 and 10. I can only find info on CANbus about resistance between the data wires, but not for the j1850. With battery disconnected, I read no resistance. I tested wires between ECM plug and j1850 plug, no shorts, and wires have continuity individually. I do have power on pin 16, and only ground on 4 or 5, don't remember. I do have ground on j1850 plug. The ECM was tested, and was told there was a software failure, and they fixed that. Just trying to make sure if there is still ECM issue before, I hook batteries up. Thanks for the input
oh, in case it matters, it is a f800, no tab for it, forgot to mention in original post.

J1850 doesn't have terminating resistors like CAN does, it's an open data line. There are a couple versions though your truck, being a 1999, should be the later one. What scan tool do you have, and does it have the heavy-duty option in it? If it's a typical automotive one, it won't read the J1850 as that's considered a heavy-duty truck and uses a different software package.

Thanks for the reply.
I had an old one, so bought a new one, it is a Thinkcar Thinkob2 20. It said it was good for both j1850 versions, but does not mention heavy duty. I will check on another new scanner.
Thanks

If you can find someone with a truck shop, you could have them, see if it will talk to their tools. J1850 was one of those odd protocols that had different implementations based on GVW splits and was carried over into the later years. There are a few others that do that as well.

Thanks for your reply.
I have other things to do to the truck before I can take it to the shop.
Thanks for all the help.

No problem, we'll be here when you get time to work on it. Thanks for using 2CarPros