How to Test a Diode. A diode is a valve that makes electrical current flow in one direction. You can test if a diode is working with an multimeter. Here's how it's done.
Change the setting on the multimeter you are using to its ohms range. It does not matter where on the ohms range you place it, but in the middle is best.
Attach the diode's cathode terminal to the "positive" marking on the multimeter. The negative part of the multimeter should be connected to the anode.
Read the meter in the ohms setting. Your multimeter should give you a low reading.
Attach the multimeter's negative to the cathode terminal and connect the positive to the anode. This is the reverse of what you just did.
Look at the new reading. This should be a high-resistance impression.