Sensors receive 3.4 volts instead of 5 volts?

So if you have a bad sensor, it will cause this issue. I would start by disconnecting the sensors one at a time while testing the voltage with each disconnection. When the voltage returns you have found the bad sensor. Can I ask if you have run the codes to see if any are stored? If not, this guide can help:

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

I would try the coolant sensor first, here is the location. Check out the images (below). Let us know how it goes.