The scan tool provides the ability to perform a "wiggle test" on wiring harnesses or components under various conditions, while observing the scan tool display. The scan tool parameters can be observed while operating the vehicle under the conditions for running a diagnostic trouble code (DTC), or when there is an engine driveability condition. If the condition appears to be related to certain parameters that can be verified with the scan tool, they should be observed while operating the vehicle. If there does not seem to be any correlation between the condition and any specific circuit, the scan tool can be observed on each position, for a period of time to verify if there is any change in the parameters that indicates an intermittent operation.

The scan tool can also be used to compare the operating parameters of a poorly operating engine with those of a known good engine. For example, a sensor may shift in value but not set a DTC. Comparing the sensor’s readings with those of a known good identical vehicle may uncover the condition.

Proper use of the scan tool will save time in diagnosis and prevent the replacement of good parts. It is important for the technician to understand the system that is being diagnosed, as well as an understanding of the scan tool operation and limitations. The technician should read the tool manufacturer’s operating manual to become familiar with the tool’s operation.