Mercedes-Benz owners may get a warning on the dashboard stating "Stop vehicle, shift to P, leave the engine running" when the battery charge status is low.

In addition, a battery symbol and exclamation mark display on the instrument cluster when the battery voltage drops below 12.5 volts. When this message comes up, various features may be turned off to conserve power.

Common Causes

This error is caused due to one of the following:

• Keeping ignition on with the engine turned off
• Leaving the lights on
• Parasitic current draw draining the battery when the vehicle is parked
• The battery is no longer holding a charge, test and replace the battery
• Too many electronic consumers connected to the auxiliary outlets
• Defective alternator or voltage regulator
• Loose battery connection or ground
• Serpentine belt damaged or off

Recharge Battery

1. Pullover and park on a safe location. Set the parking brakes and place the transmission in Park.
2. Disconnect all the electronic devices and charges connected to the auxiliary port and cigarette outlet. Turn off as many electronic consumers (radio, climate control, lights if it is safe, etc)
3. Keep the engine running in idle until the message disappears. Typically between 7 to 15 min.

The error message should turn off after approximately 10 minutes.

Another solution is to charge the battery with a trickle charger. You don't need to keep the engine running. This method works if the vehicle is parked for an extended time.

Connect a charger to the battery positive and negative jump-starting posts in the engine bay. Or disconnect the battery and charge it.

If the error message keeps coming up too frequently, locate the battery, and check the negative and positive connections. Make sure there is no corrosion.

If corrosion is present at the battery posts, use a battery terminal brush to clean them.

The next step would be to test the charging system.

Visit car parts stores such as AutoZone or Advance Auto Parts to perform a free charging system test. 

If your mechanic is having a difficult time narrowing down this problem it could be a parasitic draw, loose connection or a defective SAM module.

Read Diagnostic Trouble Codes

The next step in troubleshooting this problem is to perform a full system scan of all the modules on your Mercedes-Benz.

For this step, you will need a scanner that can read Mercedes-Benz modules. Generic OBD2 scanners are not much help but there are a few popular scanners such as iCarfot for MB and Foxwell for Benz.

Perform a full system scan to find out which modules have fault codes. Next, to the fault code, you will also find a short description of the problem.