The GM is allowed to use a Destiny Point to upgrade the difficult of any check, regardless of the situation.
That way you can get at least one challenge dice on your check.
Also note that some specific weapons also upgrade the difficult on this check, while others will add setback die to the check.
A character that recieves a critical injury might have his difficulty dice upgraded, such as the Blinded condition:
Blinded: The target can no longer see Upgrade the difficulty of all checks twice. Upgrade the difficulty of Perception and Vigilance checks three times.
Keep in mind that simple checks will hardly, ever, use a challenge dice, those are reserved for situations and enemies to will put your action at risk.
That rule is there merely to cover a situation where the GM may want to increase the risk of something really bad happening, which is the purpose of the destiny point upgrade.
Note also that pretty much all skills mentions what happens if you roll a despair, but few of them actually have rules that specify how you will obtain a challenge die on that check (knowledge skills, for example).
If you are a professional mechanic, this should hardly ever happen, the most that can happen is that you fail to attach it, which might be caused by lack of ability, proficiency, or setbacks that got into your way.