Narrative:

Yesterday morning; I read in the [company] daily email updates; that aircraft X had the APU bleed valve put back on deferral. We had this same problem [previously]. However; we also had a cas message displayed on both pfds. Maintenance did not know how to address the cas message; and wanted to defer the APU bleed and dispatch the aircraft. When toggling through the cas selection prompts on the mcdu; we were able to determine that the cas message was due to the #2 EICAS displaying the following messages: a-i wing fail; bleed 2 fail; and bleed 1 fail. It should be noted that the APU bleed could be cycled on-off and it responded; accordingly. When we refused to take the aircraft with the cas message; maintenance came out to the aircraft and was able to reset the power; and all faults cleared.a review of the aircraft logbook showed that the APU bleed had been previously written up several times. The APU bleed is not the problem. The #2 EICAS is seeing an erroneous bleed leak; and this is causing the x-ing out the bleed valve (if were it an actual bleed leak; the APU bleed valve would not be able to open up when commanded to do so).after finding that the APU bleed was unnecessarily put back on deferral; I tried to reach out to maintenance-control; but they were too busy to take my input.my concern is this: we have an aircraft that was improperly deferred and is flying around with an illegal deferral. Almost as important; we have a much-needed system which is on deferral; yet the system is completely operative.put out some type of advisory and/or memo to all maintenance personnel; on how to accurately troubleshoot/diagnose an EICAS miscompare.

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Original NASA ASRS Text

Title: An EMB-175 First Officer reported that the APU bleed was unnecessarily deferred when other pneumatic system faults were displayed on EICAS.

Narrative: Yesterday morning; I read in the [company] daily email updates; that Aircraft X had the APU bleed valve put back on deferral. We had this same problem [previously]. However; we also had a CAS message displayed on both PFDs. Maintenance did not know how to address the CAS Message; and wanted to defer the APU Bleed and dispatch the aircraft. When toggling through the CAS selection prompts on the MCDU; we were able to determine that the CAS MSG was due to the #2 EICAS displaying the following messages: A-I WING FAIL; BLEED 2 FAIL; and BLEED 1 FAIL. It should be noted that the APU bleed could be cycled ON-OFF and it responded; accordingly. When we refused to take the aircraft with the CAS MSG; Maintenance came out to the aircraft and was able to reset the power; and all faults cleared.A review of the aircraft logbook showed that the APU bleed had been previously written up several times. The APU bleed is not the problem. The #2 EICAS is seeing an erroneous bleed leak; and this is causing the X-ing out the bleed valve (if were it an actual bleed leak; the APU bleed valve would not be able to open up when commanded to do so).After finding that the APU Bleed was unnecessarily put back on deferral; I tried to reach out to Maintenance-Control; but they were too busy to take my input.My concern is this: we have an aircraft that was improperly deferred and is flying around with an illegal deferral. Almost as important; we have a much-needed system which is on deferral; yet the system is completely operative.Put out some type of advisory and/or memo to all Maintenance personnel; on how to accurately troubleshoot/diagnose an EICAS miscompare.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.