Next thing you can do is tune-up the oscillator card, you need the service terminal to do that and the crown service manual.

Thanks, water level is good and battery fully charge, also test truck with another good battery and still gives code 27. Also I replace the transistor, could I have a bad transistor can it cause code 27, I never seen this, any advise

I suggest that you connect your meter leads to the battery cables and watch the voltage as you drive either direction.

More than a 20% decrease in voltage when a motor is energized indicates a seriously depleted battery.

I'll also suggest that you take a look at the water levels for each cell.

Lots of people ignore battery maintenance.