What are the steps to replace the AVR and would it solve error 1603?

Replacing the AVR involves disconnecting the generator from power, locating the AVR, disconnecting its wiring (carefully noting the connections or taking photos), removing the old AVR, installing the new AVR, reconnecting the wiring as it was, and testing the generator. Refer to your service manual for specific instructions. Replacing the AVR may resolve the error if the AVR is the root cause, but if the control board is faulty, replacement may not fix the issue.