Ultrasonic Sensor Serial Output Grounding Issue
My first reaction:

Try a high side switch to toggle the power to the 1043 instead of the current MOSFET configuration.  This will preserve your ground reference for the serial communication.

Or, for a quick test, hard-wire the 1043 to be 'On' all the time and see if the problem goes away.

You can hard-wire the 1043 to be always 'On' by:


Removing the MOSFET1
Connect the GND terminal of the MB1043 to the negative terminal of your batteries.








simulate this circuit &ndash; Schematic created using CircuitLab