B757 Undifferentiated or Other Model
Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument
Flight Crew Total 16649; Flight Crew Type 13269
Troubleshooting
Aircraft Equipment Problem Less Severe; Flight Deck / Cabin / Aircraft Event Other / Unknown
General Flight Cancelled / Delayed; General Maintenance Action
Aircraft
At [the gate] performing preflight duties for [our flight]; APU was started and external power was deselected. FO (First Officer) went outside to perform walk around and observed smoke from APU tailpipe and was told by ramp personnel that smoke was coming from APU. FO returned to cockpit and informed me. There was no APU fire indication. I went to observe and was met by MX personnel at jetway. The smoke had subsided but was told by MX that there had been excessive smoke. I returned to cockpit with MX and APU had Auto Shutdown in last minute or so. I made PA and told pax to deplane the aircraft through jetway to Terminal area. There was no smoke in cabin. MX positioned at APU tailpipe with fire extinguisher and informed [Flight Department]. MX informed me extinguishing agent was used in tailpipe. MX made logbook entry of APU SMOKE and Auto Shutdown. I discussed aircraft with Dispatch and refused aircraft.
B757 Captain reported an APU malfunction upon start up at the gate.