How to Check Mercedes Battery / Alternator Voltage

DIY Cost: $0
Est. Time: 10 min
Difficulty: Very Easy

This is a step-by-step informational guide showing how to check the voltage on a Mercedes via the instrument cluster. 

If you are looking to test the alternator itself to determine if it is bad, follow this guide. 

Procedure

  1. Get into the car and close the door. 
  2. Use the buttons on the steering wheel to display vehicle speed or temperature on the cluster. 
  3. Put the key in the ignition, and turn to position one (I)(right before you start the car)
  4. Hit the reset button 3 times quickly. The reset button is on the side of the cluster. 
  5. You should see a value of VB: 12 volts or more on your dash and hear a beep.  This value represents the voltage coming from your battery.
  6. Start the engine to check the voltage from the alternator. 

Alternative Procedure

The steps may be different in more modern Mercedes cars (W212). If the above fails, try this:

  1. Get into the car
  2. Put the key in the ignition, and turn to position two, right before you start the car. 
  3. Hold the call button, and the “ok” button on the left and right-hand sides of your steering wheel simultaneously to enter the hidden menu
  4. You should see the options: 1. Vehicle data, 2. Roller test, and 3. Assyst plus
  5. Click “OK” on number 1, vehicle data.
  6. You should see your battery voltage immediately displayed on the screen

When you first see the voltage on display, you are seeing the battery voltage. Afterward, you can start the engine and check the alternator voltage. 

What does it mean if my dash displays a figure less than 12 volts?

If your dash displays any figure less than 12 volts, you need a jump start. 

I started my car after this, and the value rose from 12 volts to 13.9 volts, is this a problem?

It isn’t a problem, as your alternator is now charging your battery. If anything, this signifies that your alternator is in good working condition.

Where is the reset button located?

It is located in the left area of your instrument cluster. 

Do I need to access the battery to get these values?

You don’t need to access the batteries to get these readings.

How to test a Mercedes-Benz alternator? 

To test the alternator on a Mercedes-Benz you will need a digital multimeter that can measure DC current. Then follow the steps in this guide.

Gary Conway, September 16, 2020

This procedure isn't correct, not for my 2004 R171 SLK anyway. You can't do step 1 above till you've done step 2! And even then it misses a step out.

Correct procedure is:

1. With the door closed, put key in ignition, turn to the first position

2. Use the steering wheel controls to display the engine temperature on the dash

3. Turn the key to the second position

4. Press the Reset button (the bottom button on the side of the instrument binnacle) 3 times

5. There's a beep, and the voltage displays on the dash. Start the engine if you want to see the voltage with the alternator running

How to Check Mercedes Battery / Alternator Voltage This is a step-by-step informational guide showing how to check the voltage on a Mercedes via the instrument cluster.  If you are looking to test the alternator itself to determine if it is bad, follow this guide.