Final answer:
Diagnosing a VSS involves analyzing the waveform pattern using a lab scope, measuring the voltage output, and potentially, but not primarily, checking the resistance and inspecting physical components.
Step-by-step explanation:
To diagnose a Vehicle Speed Sensor (VSS) using a lab scope, the best approach is to analyze the waveform pattern. This is because VSSs typically generate a waveform that corresponds to the speed of the vehicle. The lab scope will display the waveform, and an examination of this waveform allows for the assessment of the sensor's performance.
Furthermore, by measuring the voltage output of the VSS while the vehicle is in motion, you can determine if the signal is within the expected range, given the speed at which the vehicle is traveling. This process includes comparing the sum of the voltages across all the resistors in each of the circuits and comparing the various current measurements within the same circuit. It is essential to use an oscilloscope to probe points with the same potential to ensure accurate measurements.
Finally, while checking the resistance and inspecting the physical components might help identify any apparent defects or problems, these methods do not provide the same level of detailed information about the sensor's dynamic performance as a waveform analysis using a lab scope.