Power source available, bus unpowered
Identify the source
Check whether GPU, APU generator or an engine-driven generator is available in the present aircraft state. On ELEC, FSS says the AC GPU icon appears only when the GPU is connected and available.
Check the selection
Review the relevant overhead control. Available and selected are different states. The ELEC page describes the APU indication as green when available and selected, and white when available but not selected.
Open ELEC
Trace source, tie and bus.
Neutral lines; inspect actual ELEC.
Trace the displayed source, tie and bus indications. FSS describes green flow lines as voltage sensed and white as no voltage sensed.
Read the figures
Check the available voltage and frequency indications and any relevant battery or transformer-rectifier status.
Read the CAS stack
Note all relevant messages, including any marked root message, before resetting controls.
Power transfer
Verify replacement power after transfer.
After an engine start or APU shutdown, determine whether a replacement source has taken over before disconnecting the previous one.
Electrical configuration
Save the source state, aircraft version and settings. Change one input at a time to identify the cause.
On the ELEC page, FSS says the DC GPU icon appears when the unit is connected and available; cyan IN USE appears when it is supplying the electrical system. For an available transformer rectifier, green indicates its switch is AUTO and white indicates OFF. Check the labels and bus indications before drawing a conclusion. FSS electrical synoptic [93].
A 7 November community report described TRU ESS FAIL and blank displays during an APU/GPU power transfer. Other users reported seeing the warning, but no cause or fix was confirmed. The original poster said switching TRU ESS from AUTO to OFF cleared the message but did not restore the displays; treat that as an observation, not a remedy. In a separate case, a user traced unexpected APU behaviour to a hardware binding that was still sending an APU command. That may help explain an APU control mismatch, but it does not explain TRU ESS FAIL. If this warning appears, note the source and switch positions, ELEC page, CAS messages and aircraft version before changing anything. TRU ESS support discussion, 7–9 November 2026 [192].
A 3 November support thread reported no fuel flow on an E170 described as version 1.1; the author later said the same happened in an E175. Cockpit N1/N2 rose, but the external model did not appear to rotate. The author checked idle levers, calibration, fuel pumps on AUTO and fuel onboard; EICAS showed no fuel flow and ITT −50°C. A clean control profile made no difference. No cause or fix was confirmed in the visible thread. This does not match the documented 1.1.0 hot-engine sequence, which starts dry only when ITT is above 120°C. If ITT is below that threshold and fuel flow still does not begin, do not assume dry motoring explains it. Check controls and CAS, avoid repeated attempts, and record the exact variant and build for support. Community-support thread, 3 November 2026 [193] · FSS Service Update 1 [2]. [93]