The phrase "to send the unit" typically means to deploy or dispatch a group or team to a particular location for a specific purpose or task. Full definition
On top of the fuel tank the fuel sending unit is not protected from road salt which causes the metal to rust over time and can possibly cause a leak. (autolist.com)
I would bet the issue is the temperature sending unit (the part on the car which reports the actual temp to the computer / gauge). (mechanics.stackexchange.com)