Hello! About 3 months ago my reverse screen went out, when I shift it to reverse on my automatic G the screen comes out black 3 weeks later my camara came back to life and was showing the screen perfectly fine. Next day I checked and the black screen came back on, Both the reverse lights come on, what or where can I check before buying new camara?

 

Black screen. Do the grid lines appear or is the whole screen totally black.

If you have the grid lines, read through this thread. More often than not it is a wiring issue rather than a dead/ dying camera.
If you do NOT have grid lines then it is likely the Camera Control Unit (CCU) but more information and diagnostics will be needed.

 

Great advice.

Grid lines means CCU is working and accepting the feed from the camera but camera is dying. No grid lines could be a fault from damage. Unsure where the CCU is in the G, I believe is away from the typical water intrusion areas.

So I would move towards a bad camera, it's possible that over time the wiring for the camera since it passes through the trunk it sees a lot of motion, any rips in the boot of the trunk can mess up these wires.

Start with the basics like @ILM-NC G37S said above.

 

Cars w/ NAV, the CCU is integrated into the AV head unit in the dash

Cars w/OUT NAV, the CCU (and XM SAT radio tuner) is located in the trunk under the floor trim (not far from the tire jack).