Engine Power Loss: Low Range Perfomance On
 

I have an 04 SRX V8 AWDa while agoI've been having problems while cruising and hitting a pot hole or a big junction on a bridge that the Check Engine light will come on and on the computer display would say Engine Power Loss: Low Range Performance On. Although lately while cruising or stop on an incline the Traction Control Lights would turn on, then it would start to misfire and the Engine Power Loss... message would come on and the entire SRX would turn off. My son has an OBD II scanner and the error message that comes up says : P0638 Thorttle Actuator. Range Performance Bank 1.

Anybody has a clue what this is ??? Or How to repair it ??? I'm afraid I don't have any warranty left and I'm a DIY type of person and if its a Relay or Sensor probably can repair it myself. THANK YOU IN ADVANCE