If you do a quick search on Google you will see a lot of posts on this topic. When you replace the screen on an iPhone 4 there is a chance the proximity sensor will not work properly once you install the new screen, particularly if you install a different color screen. Since we talk to hundreds of repair shops on a regular basis we have some information on this topic that I will share with you here.
First, its important to know the issue is specific to the iPhone and not to the replacement screen itself. Its been reported many times by our repair shops that a certain iPhone 4 will not work with screens that work just fine in other iPhones and they try screen after screen without success on one particular phone.
I dont know exactly why one particular iPhone 4 will have a proximity sensor issue and other ones do not, but, one of my favorite repair shops is sure it has to do with the foam that surrounds the ambient light sensor and proximity sensor. Of the two sensors above the ear speaker, the ambient light sensor is the one on the left, and the proximity sensor is the one on the right. The ambient light sensor is used to automatically dim the screen when you are in low light conditions. The proximity sensor is what disables the screen when you put the phone to your ear. He thinks the foam will stick the the back of the broken screen sometimes and this is what causes the issue. It sounds logical to me.
I think this problem has been hard to nail down because there can be multiple reasons why a phone may have a proximity sensor issue. We know Apple has recently made changes to the proximity sensor window on the latest version of the iPhone 4. They changed the sensor window from one large opening to two smaller openings. They have also released multiple proximity sensor related software updates over the years.
The good news is that there is always a remedy. The four most popular ways I have heard to get the proximity sensor to work again are:
- The Sharpie method. For this method you take a permanent black marker and color the back side of the proximity sensor window on the iPhone 4 Screen. It may take a few layers to be sufficient. This works particularly well on older versions of colored screens where the sensor window looks more like a perforation. I can personally confirm this method has worked for many of our repair shops.
- The iPhone 4 Proximity Repair Lens. This is a tiny lens that you put over the proximity sensor before you install the iPhone 4 Screen. I can also personally confirm this works but it does require that you have this part on hand in the event you do have an issue. We sell the iPhone 4 Proximity repair lens for less than $5.
- The foam method. If the foam pad around your iPhone 4 ambient light sensor and proximity sensor is damaged during the removal of your old iPhone screen you can try to replace it. Some people have had success even using black electrical tape. The goal is to make sure there is something in between the sensors to make sure they are not interfering with each other
- Software restore. It has been theorized that when you restore the iPhone it resets the Proximity sensor to work under the new condition of a slightly different Sensor window.