Hello @email, couple of more questions we'll have to know before we can help:
1. Which Dexter Industries robot are you working with, and which version number?
2. Which operating system are you running on your Raspberry Pi?
3. Which version of the Raspberry Pi are you using?
4. To confirm, you are using the Grove Ultrasonic sensor correct? What version dos it say on the sensor?
Thanks! Can't wait to offer some guidance on this!