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Home >> Mercedes Benz >> 2021 >> A220 Base >> Repair and Diagnosis >> Engine Performance >> Engine Control Systems >> Electrical System - Engine - 177 Chassis >> Testing & Repair >> Test Alternator Diodes - AR15.40-P-9301-02MFD

Test Alternator Diodes - AR15.40-P-9301-02MFD

Engine 260 in model 118, 177, 247 

except code B01 (48V technology) 

Engine 282 in model 118, 177, 247 

except code B01 (48V technology) 

except code ME08 (Hybrid drive 75-84 kW VARIANT (INCLUDING PLUGIN)) 

except code ME10 (Hybrid vehicle (plug-in, PHEV)) 

WARNING Risk of accident  from vehicle starting off by itself when Engine running. Risk of injury  (bruises and burns) resulting from working on the Engine while it is being started or when it is running. Secure vehicle to prevent it from starting off by itself. Wear closed and snug-fitting work clothes. Do not touch hot or rotating parts. AS00.00-Z-0005-01A
  Notes on safety-relevant components   AH00.00-Z-0019-01A

Shown on model 177 with engine 608 

G15489027Courtesy of MERCEDES-BENZ USA
  1. Connect engine tester with oscilloscope (030).
  2. Start engine.
  3. Switch on low beams.
  4. Assess diode harmonic content at 3, 000 rpm (engine speed).

    IMPORTANT It is not possible in this test to assess the exciter diodes.

  5. Switch off low beams.
  6. Switch off engine.
  7. Disconnect engine tester with oscilloscope (030).

An example: Harmonics, if diodes are OK (peak stresses possible but of no significance) 

G13845508Courtesy of MERCEDES-BENZ USA

Example: Harmonics when a positive diode is defective (example) 

G07649787Courtesy of MERCEDES-BENZ USA

Example: Harmonics when a negative diode is defective (example) 

G13845510Courtesy of MERCEDES-BENZ USA