Edited by WisdomAugust at 2017-9-20 09:23
Enter the scope - it pictorially shows the changing voltage over time, drawing a trace that accurately depicts the pattern of voltage variation. In fact a scope is the only way that you're going to be able to look at signals coming out of camshaft and crankshaft position sensors, speed sensors and ABS sensors, amongst others. And it's also the only way that you're going to be able to see the signals going to injectors, idle air control valves, boost control solenoids, auto trans pressure control solenoids, and so on.
Traditionally, scopes have been used by mechanics to look at primary (low voltage) and secondary (high voltage) ignition signals. And that's a valuable use for a scope. But these days a scope is far more likely to be used to look at inputs and outputs of the ECU. In fact, most good factory workshop manuals now show sample scope traces, so that you can use a scope to quickly find if the output signal from the sensor or ECU looks as it should.
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