I had the check engine light pop on a couple of weeks ago, so I decided to take a look at the computer to see what was going on. But the ECU I have is completely different than what I'm seeing in examples posted in the shop manual, and on other people's pictures posted here. There is no dial or switch, as far as I can tell. There is a torx style screw at the bottom of the unit, but it seems to secure the PCB inside the plastic shell, not control the on/off of the diagnostic mode. I'll post pictures as soon as I can.

Without seeing the unit, do you guys have any idea? At first I thought maybe it's aftermarket, but that doesn't make much sense to me.

Strange!! What truck do you have? The hardbody pickups have the ECU in a different location than the Pathfinders.