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mercedes benz battery drain problem

Mysterious Battery Drain

Battery Drain

Does your Mercedes-Benz battery slowly drain? Battery is dead every morning? Does the Mercedes-Benz battery die when you have the car parked overnight or leave it parked for a few days? This step by step guide will explain  how to troubleshoot this problem, the basics of battery drain problems, why the battery dies overnight, most common trouble spots. You try to start your Mercedes-Benz and the car is either completely dead or this happens: 


Battery drains happen when electronic equipment (consumer units) are constantly drawing current from the battery while the car is parked. One simple example is when lights are left on overnight. But it’s not always as simple as that. While the electronic equipment in your car should not draw any current when the car is parked there are exceptions such as the security system in your car. Even those systems that stay on all the time, draw very little current typically less than 50 milliampere, and should not drain the battery.

A defective electrical system, Control Unit or a fault on the CAN Bus (Controller Area Network) are also causes that can cause your Mercedes-Battery battery to die.

Tools Needed

To troubleshoot the current draw, you need a multimeter that can perform current reading. The multimeter should be able to read at least a 10 amp current. Multimeters are very inexpensive and be purchased for under $20. The Mastech Digital Multimeter is what we use in this guide, it is capable of reading currents and you can buy it online, click here to check price on Amazon.

Top 7 Systems that Cause Battery Drain Problems

  1. Seat Control Module / Power Seat Motor
  2. Audio System /AGW/amplifier
  3. Radio/ CD changer/ navigation unit
  4. Lights including light in the glove box
  5. Heated Seats Module
  6. Proximity Key / Keyless start
  7. Aftermarket alarm

Before you start troubleshooting battery drain problems

  • Make sure you have a fully charged battery. 
  • Make sure you have the radio code written down. You may be required to enter the radio code after this test.
  • You may be required to perform a window and sunroof synchronization.
  • If you are going to keep any of the doors open, manually press the door switch. Find a way to secure the switch pushed in. Use a screwdriver to lock the door latch.
  • Manually press the door switch. Find a way to secure the switch pressed. Use a screwdriver to lock the door latch.
  • If you have a fuse box in the trunk, open the trunk but place the latch in locked position.

How to troubleshoot Mercedes-Benz battery drain

Step 1

Make sure you have a fully charged battery. If your battery is over 6 years old, you should consider replacing it to avoid further electrical nightmares. You can save on the cost of the battery by purchasing it online. For example,  see this list of AGM Group 94 batteries for Mercedes-Benz on Amazon.  Turn off the lights. Make sure the dome light is off. Remove any accessories you may have plugged into the auxiliary outlets. Remove the key from the ignition and let the car sit for at least 15 minutes. In some models you may need to wait up to 30 minutes for all the electronic systems to go “to sleep”.  This will allow the car to shut off any electronic consumers that stay on for a brief period after the car is parked.Turn off headlights mercedes benz

Step 2

Locate the battery in the trunk or in the engine compartment. Remove the negative battery terminal so that we can connect the multimeter in series as shown in the next step.

Step 3

Turn on your ammeter and set it to reader currents on the A setting. Connect one test lead to the battery post and the other to the negative battery cable. You should see a current draw of less than 0.1 Ampere or 100 milliamps. If your read is over this value we need to do further troubleshooting. The reading should ideally be under 0.05 ampere.

Step 4

Locate the fuse box in your car. Disconnect the fuses one at a time. As you remove each fuse you should check the amperage reading on the multimeter. If the multimeter reading is still high, reinstall the fuse and go to the next fuse. Continue removing and reinstalling all the fuses one at a time, until you pull one that makes the multimeter reading drop to below 0.5 A. Once the reading drops below 0.5 ampere, you know that the circuit protected by that fuse, is drawing too much current. Then look up on the fuse chart to find out which electrical system that fuse protects. For example, it may be the fuse for the seat control module. Next, you will need to even troubleshoot or replace the seat control module. You may want that fuse removed until you replace the defective parts that are causing battery drain.mercedes benz battery drain problem

Conclusion

The vehicle must be resynchronized or otherwise normalized after performing this test or anytime you disconnect and reconnect the battery. To resynchronize follow these steps: Open and close the sliding roof, power windows. As the windows and the sunroof reach fully open / fully closed positions, continue to hold the switch down or up for 5 seconds. The steering angle sensor must be reset by turning the steering wheel to full left and full right with the engine running. Clear the BAS/ETS/ESP and other instrument cluster warnings.  Follow the direction in the owner’s manual to set the clock and any other settings that may have been reset during this test.

If your Mercedes-Benz battery dies, read this article to learn how to jump start your Mercedes-Benz the right way. 

 

Things to keep in mind

You should eliminate these potential problems before you dive into troubleshooting the battery drain problem.

  • Make sure no interior or exterior lights are left on during the night. Make sure no lights in the trunk are staying on when you park the car.
  • Check the battery terminals and ground connections. Clean battery post terminals. Use a battery terminal tool to clean the battery posts and terminals.
  • Make sure you don’t have an old battery. Older batteries should be replaced due to age and wear. Perform a battery load test and inspection. AutoZone or Advance Auto Parts will do a battery test for free.
  • You should do a visual inspection of the battery. Make sure the battery housing is not distorted. Make sure that all the caps are still on the battery. Check for any leakage if you have older lead acid battery. Absorbed Glass Mat (AGM) batteries  are sealed and you don’t need to worry about leakage. AGM type batteries is what newer Mercedes-Benz cars use.
  • Voltage Regulator may be defective and needs replacement.
  • Test the alternator. Make sure it is generating enough amperage.
  • Check that the glove box light does not stay on when the car is parked. The easiest way to check this is to open the glove box after the car is parked for a couple of hours. Place your hand near the glove box light bulb and feel it if it is warm. Be careful not to burn your hand.
  • Aftermarket alarm system. Aftermarket alarm system are very often the cause of battery drain. They often can discharge a fully charged battery within days. So if you have one of these systems installed check that first. Maybe disconnect it for a few days and see how it goes. Note that often times they are connected to a live battery source with an in-line fuse, therefore the test performed in this article may not catch the problem. Locate the alarm fuse, remove the alarm system fuse and test the current draw for the alarm. It should be less than 0. 1 A.
  • Proximity key allows you to walk up to the car and unlock the doors while the key is still in your pocket. A radio receiver in the car continuously listens for wake up signal from the key. As the car receives a signal in the assigned frequency it wakes up to validate the key. This causes current draw for several seconds. If the car is left parked in high pedestrian traffic areas this could be a problem. It may cause the battery to drain within a couple of days in some models. Try to turn off the proximity key function in your car by looking up the instructions on the owner’s manual.

Applicable Models

A Class W168 1997-2004 A160 CDI A180 CDI A200 CDI A170 A200
W169 2004-2013 A160 CDI A180 CDI A200 CDI A170 A200
W176 2012-Present A160 CDI A180 CDI
B-Class T 245 2005-2011
T 246 2011-PRESENT
C-Class W 202 1993-2000 C 220 C 230 C 240 C 280 C 36 AMG C 43 AMG
W 203 2000-2007 C 230 C 240 C 280 C 320 C 350 C 32 AMG C 55 AMG
W 204 2008-2014 C 250 C 300 C 350 C 63 AMG
W 205 2014-PRESENT
W 120 1953-1962
W 110 1961-1968
W 114 1968-1976
W 123 1976-1986
W 124 1984-1995 200D 230 e ce d te 260 E 280 300 E 300 CE 300 D TE E 320 400 E E 420 500 E
E Class W210 1995-2002 E 320 E 420 E 430 E 55 AMG E 300 Diesel
W211 2003-2008 E 200 CDI E 280 CDI E 300 E320 E230 E 280 E 320 E 350 E 500 E 550 E 55 AMG E 63 AMG
W212 2009-2016 E 200 E 250 E 300 E350 E 500 E63
W213 2017 – Present
S-CLASS W 126
W 140 1993-1999 500 SEC 600 SEC S 500 S 600 CL 500 CL 600
W 220 2000-2006 S 350 S 430 S 500 S 600 S 55 S 65 AMG
W 221 2006-2013 S 550 S 600 S 63 AMG
W 222
CLA-CLASS C 117
CLS-CLASS W 219 2005-2011 CLS 500 CLS 550 CLS 55 AMG
W 218 2012-Present CLS 250 CDI CLS 350 CDI CLS 300 CLS 350 CLS 550 CLS 63 AMG
CLK-CLASS
208 1998-2003 CLK 320 CLK 350 CLK 500 CLK 550 CLK 55 AMG CLK 63 AMG
209
207
CL-CLASS W 126
W 140
W 215 2000-2006 CL 500 CL 600 CL 55 AMG CL 65 AMG
W 216 CL 550 CL 600 CL 63 AMG CL 65 AMG
W 217
SLK R 170 1998-2004 SLK 230 SLK 320 SLK 32 AMG
R 171 2005-2009 R171 SLK 280 SLK 350 SLK 55 AMG
R 172
SL 129 1990-2002 300 SL 500 SL SL 320 SL 500 SL 600 SL 55 AMG SL 63 AMG SL 65 AMG SL 280
R 230 2002-2012 SL350 SL500 SL55 AMG SL600 SL65 AMG SL550 SL55 AMG
R 231 2013-Present SL350 SL400 SL550 SL63 AMG SL65 AMG
R-CLASS V 251 2006-2009 R320 CDI R 320 BLUETEC R 350 R 500 R 63 AMG R 300 CDI
GLA-CLASS 156
M-CLASS W163 1998-2005 ML 320 ML 350 ML 430 ML 500 ML 55 AMG
W164 2006-2011 ML 320 CDI ML 320 BLUETEC ML 350 ML 500 ML 550 ML 63 AMG
W166 2012-Present ML350 ML400 ML550 ML63 AMG ML250 Diesel
GL-CLASS X164 2007-2012 GL320 GL350 GL450 GL550
X166
G-CLASS W460
W463 1978-2009 G 290 G 300 D G 320 G 350 G 500 G 550 G 55 AMG

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