Final answer:
A monitor that has not run to completion will indicate an error code on the scan tool.
Step-by-step explanation:
A monitor that has not run to completion will indicate an error code on the scan tool.
When a monitor is not complete, it means that certain parts of the vehicle's emission control system have not been tested yet. The scan tool communicates with the vehicle's onboard computer to retrieve diagnostic trouble codes (DTCs) which indicate specific problems or malfunctions in the system.
For example, if the oxygen sensor monitor has not completed, it may indicate a fault with the oxygen sensor or the circuit associated with it.