sensors quastions in my cherokee 2000

my engine light is on ,I went to my garage i deal with and he checked the car he discovered with the (ODBII) three codes with three sensors that i have problem with :
1- P0113 IAT sensor voltage high (Intake air temp. high)
2- P0118 ECT sensor voltage too high (Eng. coolant Temp. high)
3- P0161 OS2 Heater Failure
i want to know what each one of them do , or how it can effect the car?
and ist serious issue or it can wait for some time to change it?
Please I need help