Chosen Solution
Hi. I replaced the screen of my iPhone 6 Plus after it getting cracked, and somehow, the rear facing camera and flash does not work in any application. In the camera app, the front facing camera works like normal, but it just shows a blank screen on the rear camera view. In the top corner where the flash is shown, it shows a warning sign and says that the iPhone needs to cool down before use, when the iPhone has no high heat in any places.
If it was working before the repair its a loose connection or it was damaged during the repair. I would open it, discount the battery, disconnect the camera, reconnect again and power up to function test. May need a new camera.
