423 is a guidance module not connected code. You mentioned you do not have guidance... Sounds like the settings in the truck thinks it does and cannot communicate with it. Like mentioned in previous response. You need a service terminal to check and correct your settings. Without the service terminal you are shooting in the dark and cannot change/correct any settings. When you buy modules (specially used) you never know what options are turned off or on. They always have to be set up to your specific options on your truck. If you have removed options, the controllers have to have the option turned off with the terminal or the display will throw fault codes and in most cases lock the truck down.