NOCTI Diesel Technology Practice Test

When testing a diode with an ohmmeter, reversing leads yields which result?

Both readings high Both readings low One high and one low reading No reading

Correct Answer:

One high and one low reading

Explanation:

A diode conducts current in only one direction, so the ohmmeter shows different readings depending on lead orientation. When the leads are placed so the diode is forward-biased, current flows and the meter reads a low resistance. If you reverse the leads, the diode becomes reverse-biased and blocks current, so the meter shows a high resistance (often “OL”). That combination—a low reading in one direction and a high reading in the other—is the expected result for a good diode. If both readings were low, the diode would be shorted; if both were high, the diode would be open or damaged.

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