Checking the Mercedes-Benz W203 Charging System

Tool:

• Voltmeter

Parts and consumables:

• Drive belt
• Engine compartment fuses (replacement identified during inspection of blown fuses)
• Alternator bearing
• Generator brushes
• Sandpaper

1. If you find a malfunction in the charging system, a generator malfunction cannot be the only reason.

Perform the following checks:

1 - Inspect the drive belt to make sure it is tight and not damaged. If damage is found, replace it;

2 - make sure that the generator mounting bolts are securely tightened;

3 - check the generator wiring and all connectors. All contacts must be reliable and not oxidized;

4 - check the appropriate fuses located in the engine compartment. If a blown fuse is found, eliminate the cause of the fuse blown and replace it (if the corresponding fuse blows, you will not be able to start the engine or turn on any of the devices);

5 - start the engine and make sure that no extraneous sounds are heard from the generator (whistling or squealing may indicate a bearing failure or brush wear);

Bearing.

Brushes.

6 - make sure the battery is fully charged. If one of the cans is damaged, the battery may draw excess current;

7 - disconnect the wire ends from the battery (negative first). Inspect the battery terminals and wire lugs. If traces of corrosion are found, thoroughly clean them. Attach the wire lugs to the terminals and tighten securely.

2. Connect a voltmeter between the positive and negative poles of the battery.

3. Start the engine. The voltage when starting the engine may drop to 8 V (at an outside temperature of +20°C).

4. Increase the engine speed to 3000 rpm. The voltage in this case should be from 13 to 14.5 V. This indicates the normal operation of the generator and voltage regulator. The alternator voltage (on-board voltage) must be higher than the operating voltage so that the battery is recharged when the vehicle is in motion.

5. Check the stability of the voltage regulator. To do this, turn on the main beam and repeat the measurement at 3000 rpm. The resulting voltage should not be higher than the previously obtained value by more than 0.4 V.

6. If the obtained value lies outside the specified value, hand over the generator and the regulator for repair at a service station.

The article is missing:

• Tool photo
• Photo of parts and consumables

Source:  http://www.auto-knigi.com/model/mb_c/7_4_6/