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I managed to find out the problem, I had a leak coming in through my windscreen and the water was running down the drivers pillar into the electrics under the floor.
There's a few MB TSBs regarding high parasitic draw due to CAN activity. We recently worked on a '18 GLA 250 in which the main battery would lose enough charge to make starting difficult (multiple attempts, weak crank) after a few days of sitting (3 or more).
Quick parasitic current measurement with car off after a few minutes only indicated a 10-20 mA draw, totally normal. Hooked up a DMM capable of recording and let it run for 5 hrs with car off and locked. Sure enough after 4 hrs there was a spike to 5 A indicating a something awoke (module/s). Spoke with a friend who indicating there's CAN monitoring function built into vehicle and it can be read with Xentry.
Sure enough, in Xentry we were able to see the interior CAN was active (not normal). This car already had the HERMES software updated and main battery replaced... all which started after mouse damage to engine harness that was replaced by dealer.
In this case, the car will need to go back to dealer and have a CAN bus recorder installed. The recorder logs all activity and is used to further diagnose why certain modules may be waking up. Definitely a complicated issue and unfortunately a lot of time to figure out.
Dear bmwpowere36m3,
I have become desperate as a vehicle I am currently working on has similar issues. Big drain(6amps) and sometimes only 2 amps...then sometimes nothing 0.03amps
It does seem sporadic. As the vehicle will shut down and go to sleep and remain that way for hours, come back the next morning and she is draining 2amps.
I have gone through all the fuses and found fuse 214 on the GLA250 active with voltage drop test across.
Also noted the engine control relay staying on and the ECU warm to touch.
I have check all the fuses under the passenger carpet too only finding drain on the ignition control module and instrument cluster.
At one stage I heard the blower fan going and thought it may be a faulty final stage unit causing the drain. However this happened once and the drain has been similar when the fan is confirmed to be off.
This afternoon I heard the engine solenoids humming as if the car is still in "ready" mode even though the vehicle has been locked for several hours and all switches latched.
I have luckily stumbled upon your forum post and was hoping you could advise on the outcome of your job if you ever found out what the issue was.
Our issues seem so similar and considering that the HERMES module is not installed in Australian vechicles I can rule that out as the cause( Hermes is only US I think)
Please could you provide some insight. It would be really be very helpful.
Same battery drain overnight after regular use. Discovered burnt wire from the Source of battery drain on '18 MB GLA45. This lead connects directly to battery B+ post but I have yet to find what it's powering. No schematics available for me to work with but this wire has definitely overheated. Your diagnostics advice welcomed.
I have been having problems with my E class.
for the past month there has been a parasitic drain it has been in and out of the dealership but it still keeps draining and its unable to start.
Its temperamental and happens at random times. I have tried checking how much power fuses are drawing and all of them seem okay.
has anyone got any suggestions?
I have owned my 2019 E300 since new and I live in the NE but I don’t drive her every day given. I put on less than 4,000 miles a year. During the first month of ownership the battery went dead 3 times and I quickly realized what the problem was, lack of use which meant lack in battery charging. I bought a CTEK battery charger and installed the cables leading to the battery. After that I put the charger on a timer which goes on at 7pm and shuts off at 7am every day and I haven’t had a days problem regarding losing battery power or parasitic drain. It’s a great and easy solution.
My 2018 E300 turned 7 years old this month and has 23k miles. I drive it 3 to 4 times a week about 2 miles each time plus an occasional trip to the airport. I leave it at the airport for 2 or 3 weeks at a time and have never had an issue with the battery. That being said, it is important to use standby mode. At other times I deactivate Keyless Go by double pressing the lock button. It prevents the fob and car from handshaking continuously when within range of each other. The fob will sleep automatically if it remains stationary for a period of time.
Note - disabling Keyless Go also prevents a nefarious individual from remotely (300 to 400 feet) cloning your fob.
2019 E 450, 2016 E350 4matic (retired), 2018 Ford Edge Sport, 2008 Porsche Boxster
Originally Posted by ua549
My 2018 E300 turned 7 years old this month and has 23k miles. I drive it 3 to 4 times a week about 2 miles each time plus an occasional trip to the airport. I leave it at the airport for 2 or 3 weeks at a time and have never had an issue with the battery. That being said, it is important to use standby mode. At other times I deactivate Keyless Go by double pressing the lock button. It prevents the fob and car from handshaking continuously when within range of each other. The fob will sleep automatically if it remains stationary for a period of time.
Note - disabling Keyless Go also prevents a nefarious individual from remotely (300 to 400 feet) cloning your fob.
Thanks for you post:
Thanks for the info about double clicking.
If you just single click, will your car go into standby mode after a few hours - or do you have to double click?
BTW, my car was built in November 2018. I picked it up in December 2019 - it is a 2019 E450. Not wanting to jinx, I am still on the original battery. I drive the car almost every day and have 45,000 miles on it.
Each spring and fall I put a battery charger on the battery - 10 AMPS. It usually takes overnight to fully charge the battery - when the battery charges senses the battery is fully charged, it automatically turns off.
Each year when I go in for inspection or oil change, whichever comes first, I ask my Indy shop to test the battery. So far so good!
My 2018 E300 turned 7 years old this month and has 23k miles. I drive it 3 to 4 times a week about 2 miles each time plus an occasional trip to the airport. I leave it at the airport for 2 or 3 weeks at a time and have never had an issue with the battery. That being said, it is important to use standby mode. At other times I deactivate Keyless Go by double pressing the lock button. It prevents the fob and car from handshaking continuously when within range of each other. The fob will sleep automatically if it remains stationary for a period of time.
Note - disabling Keyless Go also prevents a nefarious individual from remotely (300 to 400 feet) cloning your fob.
You mentioned something you refer to as “Standby Mode”. What exactly is it and also do you live in CA or FL? The reason I ask is batteries will retain their charge in warmer climates.
Standby mode is described in your Operators Manual. Basically, it shuts down all systems in the vehicle to conserve battery power. I live in Florida at the location shown when I post.
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