To get to the timing belt the shop probably had to disassemble the air intake pathway, which may have required removal or repositioning of the sensor, unplugging the pigtail, etc.
Hard to tell, though, as I'm not all that familar with the Trooper.
In any event, though, unless it shows obvious signs of damage, chances are is an AW DAMMIT! failure, which is the failure that invariably happens either on the way home from, or soon after getting the car back from, the shop. Those are the ones caused by the gremlins that live in the garage and come out when the mechanic isn't looking.