Thanks for the quick responses. Your posts tell me that at least this doesn't seem to be a common problem with the Enertia. With only 470 miles on my Enertia I was worried this might be common and unfortunate.
I did contact Brammo and they instructed me to email my diagnostic logs from Friday to them. They took a look and replied
"there is no information identifying a specific component failure. A D4 error code typically indicates an issue with the motor controller. It is possible that there may be a blown fuse or a faulty wire connection to or from the motor controller. Have you checked the fuses?"
My thanks to Brammo for responding to me so fast as well.
I'm going to charge the Enertia tonight to see if that will fix the problem. It's definitely not related to moisture as I store the bike indoors and I rode it on the first 80 degree day in Boise with clear skies. It's been sitting inside for 5 days now with still no luck avoiding the D4 error on startup when the drive should engage. Another odd symptom is that the chain currently does not move as freely as it did before when manually pushing the bike around. There is a small catch in the wheel turning and a clicking sound I've not noticed before. Perhaps the motor controller is engaged but without power.
I'll keep you posted on anything I find out. Right now the bike turns on, power is available to everything, but when the drive should enable the LCD instead shows the D4 warning. If I get any resolution soon I'll also post to the wiki what I've learned. Thanks