It's tricky to detect the defective CV joint, especially if you are not a mechanic. The simple way to tell a bad CV joint, whether left or right is by listening for clicking and knocking sounds while steering. If the clicking sound happens when you turn left, the right CV joint is bad. And if it occurs when you turn right, the left CV joint is bad. We'd recommend you change both CV Axles if one side is damaged. But if you detect a damaged CV boot, change that side alone; you should be fine.