Line following object avoidance robot.

I was able to pick up a code online but the code doesn’t run smoothly. After a great deal of trial and error the voltage supplied to the sensors was around 4v which made the ultrasonic sensor not able to function. I believe this is caused by either wiring or the code itself but I checked the Vin for the arduino and shield and they were above the minimum recommended voltage I’m using 8 batteries as my power supply. I’m looking for help to finish the project