Why is my Jeep Grand Cherokee parksense not working?

First, it's important to note that the Jeep Grand Cherokee's Parksense system won't work if the key is not in the ON position -- if You're "testing it out" in accessory mode, You won't have much success. It sounds basic and commonsense, but You wouldn't believe how many drivers were simply mistaken about the way the system works. With that said, if Your system really is failing, the most common issue is a d***y or broken sensor. First, clean them to the best of Your ability. Then, inspect any wiring, since this is a particular weak point in the Parksense system. Finally, You can test a sensor's resistance with a digital multimeter, and hopefully You'll see if it's in proper working order.