Check Diodes of Generator

Workshop equipment/MB test instruments
WE58.40-Z-1011-06A Engine tester with oscilloscope






Shown on model 202
Connection diagram

1 Connect engine tester with oscilloscope (030).


NOTE: Model 163: connection from generator (G2/B +) to battery (G1/+), different cable color (25 sq.mm rt).


NOTE: Model 129: connection from generator (G2/B +) to battery (G1/+), different cable color (10 sq.mm wsrt).


2 Start engine.
3 Switch on low beam.


NOTE: it is not possible to assess the exciter diodes during this test.


4 Assess diode harmonic pattern at 3000 rpm (engine speed).


NOTE: Model 129 with engine 119 up to VIN 1F 032 589:
If problems exist with power system, test idle speed increase independent of battery voltage (see Diagnosis Powertrain Management, System Diagnosis.)






Diode harmonic pattern okay (peak values possible although insignificant) (example)






Harmonic pattern when a positive diode is defective (example)






Harmonic pattern when a negative diode is defective (example)