P0115 indicates a problem with the coolant temp sensor readings.
P0081 appears to not apply to the Santa Fe. It's listed as "Intake valve
control solenoid, bank 1." As the Santa Fe doesn't have variable valve
timing, I don't see how this would apply.
U3118 also should not apply as the '01 Santa Fe doesn't have CAN
communication between computers. My code list is old enough that it
doesn't list any U codes.
I also have no description for a C0300. Any C code would be a traction or
ABS problem, so if you don't have traction or ABS, it doesn't apply to your
I largely suspect the code reader used is having some difficulty
communicating with your vehicle. You may wish to try a different reader.
P0115 seems believeable. The others are highly suspicious.