Mercedes-Benz W639 battery and charging warning light on
W639 battery light flickers on and off, what is the fault?
The most common cause is a worn alternator, for example worn-out brushes. Another possible cause is the power cable between the starter motor and the alternator, which has oxidised through inside its protective sheath, so it is worth checking the condition of the cable.
Why do warning lights come on in the instrument cluster when the alternator is not charging?
The drop in battery voltage can turn on the engine warning light as well as the ESP and ABS lights. The light may go out by itself when the voltage recovers. After the alternator is replaced the symptoms have usually gone away.
The light is on after replacing the alternator, what should I check?
A cheap aftermarket alternator may not fit the car, so choose an alternator that matches the original part number. The charging regulator can also be faulty separately.
Why does the automatic headlight function stop working with a charging fault?
With a charging fault the instrument cluster may report that 61 is missing, and then the automatic light function also stops working. Repairing the alternator will probably restore normal operation.