Uu code on kohler 18res generator - Kohler 12 kW Emergency Power System - 12RES-L

SOURCE: UU undervoltage kohler 20kva

call koler but ui think is meant high heat as in the thermal circut is shuting you down or low oil
could be a couple of things best bet call kohler

SOURCE: UU lowvoltage error code residential generator

Could be the battery voltage. If your battery is not charging properly, the controller on the unit can do some funky things! Exactly how long does it run for? Is this in auto or manual mode?

SOURCE: I have a Kohler 12RESM1 propane generator with oc/uu code

I am getting the same exact problem and errors with my 12RES Kohler generator. It will try to start using a remote switch but fails. Then it will start using the switch at the generator. The error code it comes up with using the remote start switch is usually OF or UU. It is less than a year old. Can Kohler Help??? Dave R.

SOURCE: Code UU

Here is the code explained direct from Kohler's manual. I'd disconnect the generator load first.
UU Undervoltage Shutdown occurs if the voltage falls below 80% of the nominal system voltage for more than seconds. Check wiring and connections.
Reduce the load and restart the generator set. —
Check wiring and Check controller configuration, system voltage
and frequency (parameter UU).

Check AC voltage and adjust, if necessary. 5.7
Replace the SCR module and test voltage again. 4.9
Separately excite unit. 5.2
Check stator continuity

See web site for manual :http://www.kohlerpower.com/onlinecatalog/pdf/tp6196.pdf

SOURCE: I have Kohler 12Res generator,sometimes

If it has a couple hundred hours or more, try cleaning the slips rings on the back of the rotor shaft. They should be very shiny and not black or polished looking.