This guide will let you know how to fix L3 Button Sprint Not Working in Call Of Duty Modern Warfare 2.
1- To fix this issue, you will need to rotate your left thumbstick in the right direction at least 30 times and then rotate it in the left direction 30 times. After this, click on it almost 30 times. Then you have to lift it up and down at least 30 times.
Now you have to move your thumbstick to the left side and then blow or use some dust cleaner liquid to clean the dust in it. If you are still having the problem, then you have to completely open your controller and clean your analog sticks.
2- If you are still facing the issue, then you have to boot up your game and press the Options button. After that, go to settings and navigate to Controller settings.
Now you have to head under the Gameplay section. Go to the automatic sprint and set it to Automatic Tactical Sprint. After that, press the left thumbstick in the forward direction and then it will start the sprint. It will completely solve your L3 button issue.