93 Volvo w/Cummins M11 won’t start. Help!

I have a '93 Volvo tandem dump w/Cummins M11 that won't start because the "Check Engine" light is on. I have changed coolant level sensor and EPS Sensor. I can't get the code because the cruisecontrol does not work. For a while last year the coolant tank leaked and when the level got too low the light would come on, beeping would start and the engine would turn off. Refilling the tank would turn off the light and the truck would start. I fixed the leak at the bottom of the tank and problem solved. A few months after that, the beeping returned, but only when I pushed in the clutch. The tank was full but beeping persisted. Nothing would happen as long as you left the truck running. This year when I went to start the truck after sitting for the winter, the check engine light would come on and truck would not start. After jacking with it for a while, the light goes off and truck starts. It will not restart if you turn it off until the next morning. That went on for a couple days. A couple days ago, I got the truck stuck and the engine died while trying to get it out and has not restarted and "Check Engine" light will not go off. Is there some type of device to get the code from the ECM like cars that is not too expensive. There is a round metal port under the driver side dash where you plug in to get code. Any help would be appreciated. :beatsme