Turn off your phone WiFi so it is only using the cell towers. No Wifi, that way your phone is acting like it is not at the wash location, and is relying only on Cellular.
If you want to use only WiFi, then put it on airplane mode, and only enable WiFi on your phone. Then you phone will connect with your local wash WiFi network.
When at the wash location, your phone may be conflicting between using WiFi and Cellular signals.
We have tried that; still doesn't work.