Starting System & Charging System (H4SO): Generator: Inspection: Diode

CAUTION: There is the possibility of damaging the diodes if a mega-tester (used to measure high voltages) or a similar measuring instrument is used. Never use a mega tester or equivalent for this test.

Check the positive diode
Check for continuity between the diode lead and positive side heat sink. If resistance is 1 Ω or less only in the direction from the diode lead to the heat sink, the positive diode is OK.

Fig 1: Checking Continuity Between Diode Lead And Positive Side Heat Sink
Courtesy of SUBARU OF AMERICA, INC.
Check negative diode
Check for continuity between the negative side heat sink and diode lead. If resistance is 1 Ω or less only in the direction from the heat sink to the diode lead, the negative diode is OK.

Fig 2: Checking Continuity Between Negative Side Heat Sink And Diode Lead
Courtesy of SUBARU OF AMERICA, INC.