Small Engine Troubleshooting Problems? Ask a Mechanic Now.
Code 1900 is Prolonged Under Voltage. This could turn out to be a very exepnsive repair. IF your unit is only 1-1/2 years old, it is still under warranty.
The best course of action for you would be to contact an authorized Generac repair facility, and have this repaired under warranty.
If you attempt to work on this yourself, you will void your warranty, and will be responsible for the cost of any parts needed.