Like true value said, check wires on grid heaters. The code you have is for a ground. I'll try to get the pin number of the ECM for you from the wiring schematic, that way you can check for continuity of the relay signal wire.Check the wires on your grid heater.
i believe there is a total of 5 grounds on the truck that need to be cleaned, and sealed periodically, cant remember where they are all at, my dad did it last time he had my truck (someone chime in). also clean up batt. terminals.check the ground next to the driver side battery too....it's on the fender under the hood.