There is no single HU in the G20, there is a HU-H unit under the dash connected to the CID, and another unit in the trunk -RAM unit.
Either of those two units is having a problem sending the video signal to the CID, the CID is having video problems or the cable between the CID and the dash unit is defective for the " NO SIGNAL" to be displayed. For sure, there is power in the CID.
