Turn off power to the circuit
Remove the diode from the circuit if possible
Set the multimeter to diode test mode
Place the red probe on the anode
Place the black probe on the cathode
Read the forward voltage drop on the display
Reverse the probes
Read the reverse measurement on the display
Confirm one direction shows a voltage drop and the other shows OL or no reading
If both directions show low resistance or a voltage drop, the diode is shorted
If both directions show OL or no reading, the diode may be open
Compare the reading to the diode type’s expected forward voltage
Reinstall the diode after testing if it is still good