If the APU is started without external power, what indication will be absent?

When the APU is started without external power, the indication for fire detection or exhaust gas temperature (EGT) will be absent due to the lack of required electrical power to operate the systems that generate these indications. Fire detection systems rely on electrical sensors that are powered on startup, and without external power or the main battery supplying voltage, these systems cannot function properly. Likewise, the EGT measurement relies on electronic sensors and instrumentation that also require power to provide accurate readings of the exhaust gas temperature.

In contrast, fuel pressure indication and battery voltage indication could still be available depending on the specific design and configuration of the aircraft's electrical systems. The hydraulic system indication generally relies more on anti-saturation systems or certain variables from other subsystems and is not solely dependent on power from the APU on startup. Therefore, the absence of fire detection and EGT indications serves as a clear signal that there is no external power to facilitate the monitoring systems required for those parameters.