ichudov,
Well Sir, you list the type and model of rig you have but not the chassis. Unless I missed it some place. If it's a Freightliner chassis, not only should you have a 9 pin diagnostic port to the left and low of the steering column but, most Freightliner chassis vehicles also have one in the rear, just above the radiator. But if you have a side radiator, I'm not exactly sure if and where, you'd have that diagnostic port at the rear. Maybe in the same area as it would be if there was a rear radiator.
But, this port of course would be for plugging into while being stationary. Also, if you by chance have what's called the Medallion Information Center in your dash, you can dial into the engine service section and find codes, if any are active or, inactive. You'd need the entrance code of four numbers to access this part of that info center. I don't know if any of this info will help you or not, just thought I'd throw it out at ya.
Scott
