That's not exactly correct. When a 536 is receiving data from a GPS device, the letters "GPS" are displayed in the top row. There is a good picture of this on Page 9 of the manual.
I did some searching to see if something similar happens on the 436 without success. I can see why it would not as the 436 display isn't as wude as tge 536.
However, you can confirm whether your 436 and GPS are communicating by doing the following. Set the zip code on your scanner to something far away which causes the systems for that far away area to load. Then connect the GPS. If you see your local area systems begin to load, proper scanner/GPS operation is confirmed.