Test alternator diodes - AR15.40-P-9301-02CW

WARNING: This page does not describe the selected car, but rather 33 other vehicles, including the 2016 Mercedes-Benz E63 S AMG, 2016 Mercedes-Benz E400, 2016 Mercedes-Benz E350, 2016 Mercedes-Benz E300, and 2016 Mercedes-Benz E250. However, it is still accessible from the selected car via links, so may be relevant.

ENGINE 156, 271 in MODEL 212

ENGINE 156, 271, 272, 274, 642, 646, 651 in MODEL 204

ENGINE 271, 272, 273, 642, 651 in MODEL 207

ENGINE 271, 274 in MODEL 172

ENGINE 274 in MODEL 205, 253 except code ME05 (HYBRID DRIVE 80KW VARIANT (INCLUDING PLUGIN))

ENGINE 276.8 in MODEL 205

ENGINE 642, 651 in MODEL 218

ENGINE 651 in MODEL 205, 253

Connection scheme model 172

Fig 1: Alternator Diodes Connection Schematic - Model 172

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Connection scheme model 205

Fig 2: Alternator Diodes Connection Schematic - Model 205

Courtesy of MERCEDES-BENZ USA

Connect engine tester with oscilloscope (030).
Start engine.
Switch on low beams.
It is not possible in this test to assess the exciter diodes.
Assess diode harmonic content at 3000 rpm (engine speed).
Example: Diode harmonics OK (voltage spikes possible, but not significant).

Fig 3: Diode Harmonics OK Graph (Voltage Spikes Possible)
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Example: harmonics when a positive diode is defective.

Fig 4: Diode Harmonics Graph (Positive Diode Defective)
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Example: harmonics, when a negative diode is defective.

Fig 5: Diode Harmonics Graph (Negative Diode Defective)
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Example: zero line, if the alternator fuse is defective.

Fig 6: Diode Harmonics Zero Line Graph (Alternator Fuse Defective)
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