The Union likely had these tunnels flushed out and ready for use if they wanted to take the planet. He used a feature on his heads up display to scan the map. But as his helmet attempted to do so there was fritzing.
Jace cursed under his breath and smacked the side of his helmet causing Shepard to jump in surprise. He then relaxed while Jace's armor's systems began operating again and successfully scanned the map. He now had a digital map in his armor.
"I am surprised your armor is malfunctioning. With how high grade it is that seems like a flaw in the design that should not have let it get off the rack." Shepard pointed out, he was clearly using the opportunity to fish for information. Although he might not have been doing it on purpose and it was just a habit.
