Codes appear how to fix?
P2108 = https://www.autocodes.com/p2108_gmc.html
P1516 = https://www.autocodes.com/p1516_gmc.html
P1518 = https://www.autocodes.com/p1518_gmc.html
All the codes are related to the throttle actuator control module, start by inspecting the module connector for water. If the connector is OK, you may have to replaced the module.