My iPhone 6 Plus back camera isn't working.The front camera works fine but the back camera shows black screen and doesn't works.

If you see a closed lens or black screen when you open the Camera app, try these steps:

1. Make sure that there’s nothing blocking the camera lens. If you’re using a case, try removing it.
2. Force the app to close, then open the Camera app again.
3. Restart your device, then open the Camera app again.
4. If your device has a front and rear camera, try both cameras by tapping . If you see the closed lens or black screen on only one camera, take your device to an Apple Retail Store or Authorized Service Providerfor more help.

Hi Sam

If you have not yet done so, it may help to update your iPhone to the latest software:

Update the iOS software on your iPhone, iPad, or iPod touch - Apple Support

Also, check whether your iPhone is eligible for the iSight Camera Replacement Program for iPhone 6 Plus:

https://www.apple.com/support/iphone6plus-isightcamera/