Q: Saturn Ion wont change to 4th gear, its an automatic. The P0700 code comes up saying transaxal module. What does this means?

Hello. The code means there is either an electrical or mechanical (hydraulic) fault in the transmission, or the transmission "controls" and in your case that fault is causing your transmission not to shift. The fault itself can range from the incredibly mundane (a mouse chewed through a wire in the electronic control segment; a harness plug connector is corroded) to a real pain the neck which would be a faulty valve or solenoid in the transmission itself (in the "valve body"), although often even that issue can be repaired without removing the transmission.

The mechanic would diagnose for an open or short in the wiring harness, a faulty transmission control module, or a transmission valve body fault including a failure of an electronically controlled shift solenoid. Although the issue you are describing is troubling, it is fairly common. For example, it is not unusual at all for shift solenoids to fail. If they do, there will be no, or possibly erratic shifting. Some car models have been more prone to this issue than others. An expert from YourMechanic could diagnose this shifting issue for you and get you on your way to a professional repair.