Generac 16KW starts then immediately shuts down with read out saying low voltage

Check the wiring from the utility through to the autostart control.; make sure all connections are solid and the wire itself is in good condition. New wire is no guarantee, several times I've had wire with a break somewhere in the reel. A non-contact voltage detector may helpful; start at the controller end, go to the other end of the wire, and see where you lose the voltage detect. It will detect voltage up to the break if you can keep the detector close enough to the wire.

check the brushes and commutator

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low voltage can be from incorrect running rpms
as it is new out of the box I suggest that you get a service under warranty to sort out any problems

gen sets have to be run at set rpms so that the voltage and cycles are correct for the applications
with the rpms as little as 100 rpms below requirement , the voltage will be down , causing a brown out which burns out electric motors and if the rpms are low the required cycles will also be off which affects electronic equipment
service the gen set and find out why the rpms are not at the set level

There are several Generac forums available:

generac forum Bing

smell the oil to see if it smells like fuel f so the carb needle valve may not be seating

DO U HAV POWER FROM GEN ?