Guys - the only thing you need for a working proximity sensor is a GOOD QUALITY glass, a working proximity sensor flex cable and the UV filter sticker. We sell the original iPhone 4 proximity UV filter sticker with the black foam from our online store
[https://mendmyi.com/parts-shop/product/iphone-4-proximity-sensor-uv-sticker-with-foam/|HERE]
You don't need anything else - just those 3.
The most common fault is to lose the UV sticker during installation. Second most common is to use a cheap copy front with a poor light filter at the top.
I'd recommend fault finding in the order:
1) Check for UV sticker
2) Try new front glass
3) Try new proximity sensor flex
It should definetly be working by the end of step 3.
Also to add - on the inside of the phone (the other side of the proximity sensor) is a little black plastic block. this plastic block holds the proximity sensor towards the front of the phone. If this is not placed properly or is missing it can affect the proximity sensor. We also can supply this spacer block
[https://mendmyi.com/parts-shop/product/iphone-4-proximity-induction-flex-plastic-spacer/|HERE]