B757 Undifferentiated or Other Model
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Maintenance
Flight Crew Diverted; General Flight Cancelled / Delayed; General Maintenance Action
Aircraft
Operated Flight ABC ZZZ to ZZZ1 and approximately 75 nm east of ZZZZZ [fix] I checked the EICAS status page and noticed ADD for the APU oil.  A couple of minutes later we got a status message stating APU oil was low.  I SATCOMed Dispatch and conferenced Maintenance Control. Decision was made to divert to ZZZ.  No emergency declared - normal arrival.  When maintenance techs were in the cockpit after arrival they stated that the APU oil was checked via EICAS as part of the ETOPS pre-departure service check.  While speaking with the tech they stated that the technician working in the tail just added three quarts of oil which they said is just 'a lot' for the APU doesn't hold much more.  APU started for a leak check and it auto shutdown twice.  It was said that there were no leaks.  The tech stated they found it strange when looking at history that no oil had been added in two months. It was theorized by maintenance that the quantity unit may have been stuck showing full when it wasn't.  Flight was re-dispatched with a different aircraft.  I subsequently found out that the oil quantity unit and oil pressure switch were replaced to fix this problem.
B757 Captain reported that a low oil level in the APU resulted in a divert. Maintenance found the APU was several quarts low and that the indicator may have erroneously been showing it was full.