Mercedes-Benz W202 alternator not charging or wrong voltage
W202 charge light is on or the battery is not charging. What can cause it?
The most common causes are worn-out alternator brushes, a faulty voltage regulator or a broken alternator exciter wire. Sometimes the cause is also a worn armature shaft or damaged diodes. The ABS light often comes on at the same time because the voltage is too low.
What is the normal charging voltage in a W202?
With the engine running the voltage is about 13.8-14.4 V, and with the engine off the battery shows about 12 V. If the voltage drops clearly below 12 V while driving, charging is not sufficient. Measure the voltage before replacing the alternator.
The voltage rises too high and the battery gets hot. What is the cause?
Usually the regulator outputs too high a voltage, for example 17-18 V, and the battery overheats. Replacing the regulator or the alternator fixes it. If the overvoltage continues, check the grounds and the alternator's thick cable.
Should I replace the alternator brushes or get a new alternator?
The brush pack comes off together with the regulator with two screws, and short or sparking brushes are worn out. On the larger 115 A alternator they are under the rear cover, so the job is harder. If charging does not recover after the brushes, replace the whole alternator.