Roy,

At the connector going to the HEGO, pin 1 is battery voltage with key on. No voltage, need to check fuse 10. Next, disconnect battery and check pins 2 and 5 resistance to battery negative cable, should reads less than 1 ohm. If resistance is high or out of range, need to check harness. Connect battery and check pins 3 to battery negative, then pin 4 to battery negative, both should read about 2.5 volts. If one is a little less or a little more that is OK. Both together need to be about 4.5 volts. Again, should they not read correctly, check harness. Last, check ohm reading between pins 3 and 4, looking for 60 ohms. All checks are made where the NOX sensor connects to the harness. Good Luck

I have same model doing that. Has been going on a year now. Have no idea, as soon as I turn it off it clears and can't trouble shoot what isn't there

I can see more specifically that code is for pre nox sensor heater error. Check battery > fuses > wiring. Good luck.