Final answer:
Technician A is likely correct in asserting that the alternator is overcharging, as a charging voltage of 17.3 volts at idle is above the normal range, suggesting a faulty voltage regulator or charging system issue.
Step-by-step explanation:
If a vehicle's charging system is charging at 17.3 volts at idle, this is higher than the typical range for a charging system which is around 13.8 to 14.5 volts. Technician A who suggests that the alternator is over-charging and that the regulator may have failed is likely correct. A properly functioning alternator should typically not exceed this range as it can lead to overcharging the battery and causing damage to the battery and other electrical components. Technician B's assertion that there is no fault because the alternator is working 'great' is incorrect in this scenario, as the excessive voltage indicates a potential issue, such as a faulty voltage regulator or some other problem within the charging system.