Test diodes of alternator - AR15.40-P-9301-02GZ

WARNING: This page does not describe the selected car, but rather 8 other vehicles, including the 2011 Mercedes-Benz ML350, 2010 Mercedes-Benz ML350, 2009 Mercedes-Benz ML320, 2009 Mercedes-Benz GL320, and 2008 Mercedes-Benz ML320. However, it is still accessible from the selected car via links, so may be relevant.

COMMERCIALLY AVAILABLE TOOLS

Number	Designation
WH58.30-Z-1016-09A	Clamp-on probe
WH58.30-Z-1046-13A	Engine tester with oscilloscope

Connection schematic between battery and alternator

Fig 1: Battery And Alternator Connection Diagram

G07253183

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

In this test, it is not possible to assess the exciter diodes.

Connect the engine tester with oscilloscope (030).
Start engine.
Switch on low beam.
Assess diode harmonics at 3000 RPM (engine speed).

Diode harmonics in order (voltage spikes possible, but not significant) (example).

Shown on the oscilloscope - diode harmonics OK

Fig 2: Diode Harmonics Graph (Diode Harmonics OK)

G07077825

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

One of the positive diodes is defective (example).

Shown on the oscilloscope - positive diodes harmonics not OK

Fig 3: Diode Harmonics Graph (Positive Diodes Harmonics Not OK)

G07077827

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

One of the negative diodes is defective (example).

Shown on the oscilloscope - negative diodes harmonics not OK

Fig 4: Diode Harmonics Graph (Negative Diodes Harmonics Not OK)

G07077828

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.