I suspect that isn't a valid trouble code in that case. U codes relate to faults on the CAN data bus. And I don't think there is any CAN on a MK1 Santa Fe, unless it's fitted with an auto gearbox.Manual Gearbox.
I think you should have the engine ECU scanned using a Hyundai specific tool rather then a generic OBD2 one.I have a AUTEL OBD2 code reader. It will start and drive but it just won't go past 2800 rpm.