Recently bought an 08 g35xs sedan w 45k on it … had it abojt a month now went to mechanic for routine check up and he told me that codes were going off even tho there’s no check engine hopefully someone can tell me what these are and what they cost to repair

 

U1000 means one of the computers isnt communicating properly there's like 7-8 one for each system, engine, transmission, abs, srs, etc.

P1815 is the MM switch on the shifter (manual shift)

P0615 could just be a weak battery. Also sort of explains the U1000.

Does it have a hard time starting or has it sat long enough to drain the battery recently?