P0620 MERCEDES-BENZ – Generator Control Circuit Malfunction

P0620 MERCEDES-BENZ Possible Symptoms

Engine Light ON (or Service Engine Soon Warning Light)

P0620 MERCEDES-BENZ Possible Causes

Battery charge,Faulty Alternator,Alternator harness is open or shorted,Alternator circuit poor electrical connection,Faulty Engine Control Module (ECM)

P0620 MERCEDES-BENZ Description

This fault code is stored in a control module when the charging system control does not perform as expected. In order to create a more efficient charging system manufacturers are now using an intelligent charging system. A control module sends a signal to the alternator depending on engine load and operating conditions. This signal is responsible for altering the alternator field current. Manufacturers can use a varying PWM, or pulse width modulation, to command and receive feedback from the alternator. A larger current flow through the field winding will result in a higher charging output voltage. A reduced current flow through the field winding will result in a lower charging output voltage. Some manufacturers now use LIN, or local inter-connection network, communication to control the alternator output voltage. Both LIN bus and PWM control can be tested using an oscilloscope. Some vehicle manufacturers offer a tool which can be used to control the alternator disconnected for the control module which is responsible for controlling it. This allows for accurate diagnosis.