Test Mercedes-Benz Alternator

Testing the alternator on a Mercedes Benz is relatively easy; it only takes half an hour, even for a beginner. This guide provides instructions on how to test the alternator on a Mercedes Benz.

We already have replaced the alternator in this vehicle, but we’re still getting the battery warning light on the dashboard; there might be other issues like poor ground connection, blown alternator fuse, and sometimes an ECU problem.

We verify if the new alternator is working, test the alternator’s positive terminal for 12 volts, and check the feed in the voltage regulator.

What you will need

Tools

• Voltmeter with an alligator clip
• Wire (optional)
• Electrical tape (optional)

Check Alternator Power

Follow these steps to test the alternator on a Mercedes Benz.

First, we will check the positive terminal of the alternator, connect the positive test lead of the voltmeter to the alternator’s positive terminal, and connect the negative test lead to the ground from here.

We read 12.93 volts, the battery voltage running to the positive alternator terminal. When the engine starts, the voltage should increase to 13 to 14.5 volts. With the engine off, the voltage should decrease to 11.5-12.9 volts.

Test Voltage Regulaor

Next, we will provide a signal voltage to the voltage regulator by hooking a wire from the battery directly to the signal terminal of the voltage regulator; we should see the voltage increase in our voltmeter; the voltage may vary depending on the voltage required to charge the battery, the signal may provide 6 volts or full load, and that is 12 volts.

Disconnect the alternator connector, connect the jumper wire to the voltage regulator’s signal terminal, and start the engine. While the engine is running, connect the other end of the jumper wire to the positive post; the voltage should increase to 14 volts.

The voltage remains the same, so we verified that our new alternator is the problem.

Reminders

• Please do not connect the jumper wire to the battery terminal for too long; remember that the signal terminal varies its voltage. The alternator might overload.
• Consider checking your vehicle’s wiring diagram before performing the same procedure because, in some vehicles, the module provides a negative signal.

Troubleshooting Charging System

One way to determine if you have a faulty charging system is by scanning your vehicle with an OBD-II scanner. One good example of a multi-system scanner is the YOUCANIC Full Systems Scanner. This scanner can read and clear fault codes from all the systems in your Mercedes-Benz. It can also perform bi-directional tests, maintenance and repair resets, etc.

We hope you find the Test Mercedes-Benz Alternator guide helpful. Check these troubleshooting and repair guides for more help on your Mercedes-Benz.