E320 2007 Battery drain issue - help to others

[mcmcmc]

Hi everyone, I'm Mark & am new on this forum. I repair cars on a daily basis & look here occasionally for common issues. Just thought I'd add a small bit of my findings from a recent job on an E320 which was losing battery power overnight.

Mercedes E320 2007 Car had been stood for a while, a new battery was needed & fitted.

After a short time of use, the battery would lose power overnight. I was asked to look at the issue.

I hooked up an ammeter to test for leakage current, removing a fuse at a time. The battery drain was 0.27 Amps & on this vehicle the systems take about 2 minutes to power down after many of the fuses were refitted, so the process was pretty tedious. I traced the battery drain to Fuse 8 in the boot compartment left hand fuse block. The fuse is 7.5Amps & is for the alarm system, but also annoyingly the one that allows the key fob to operate. Therefore to lock the car I had to use the central locking button, then the key blade on the driver's door. Same to unlock, using the key blade. The next step would be to investigate the alarm siren as I assume it has corroded inside, causing the drain. However I wasn't asked to go further with the job having found the main issue.

I hope this thread saves someone a lot of trouble as I couldn't find this as being a common issue from a few searches.

 

[Glenzil]

Just to add to Marks post, the battery on my 2016 GLC250D x253 will go flat over a couple of days despite being used, albeit fairly short trips. I fitted a new battery after buying the car last year so I had a known good battery. Anyway I assumed I had a parasitic drain so I did some tests with my ammeter in series with the negative lead on the battery and I think I've found the problem. The following are the amp readings as the car slowly goes to sleep:

1. initially on switching off the car and locking it the current drain is a massive 13 amps for a few minutes.
2. It soon drops to 10A and stays like that for another 10 mins.
3. Then it drops to 6.5 Amps for another 10mins or so
4. It took roughly 3/4 hour in total to drop to 30mA.

The problem is that if you unlock the car then lock it again it will go through the same process so just going in and out of the car and a few short trips and the battery will be flat. It seems to me that it is taking way too long to go to sleep, as far as I am aware it has had all the various recalls so I'm wondering if there a software update it hasn't had.

I had a dc clamp meter on the lead at the same time as using the ammeter just as a comparison as I've read many comments on using one and how inaccurate they are. Well mine was a cheap one and yes it was different by 200mA, however if you had a hefty current drain it would be more than adequate to identify that.

 

[mcmcmc]

Yes Glenzil that drain is way longer before dropping & higher than the way the E320 behaved. The initial drain was about 3.5-4 amps & took a few mins to drop in a few different stages. I too tried a DC amp clamp but as with you i found the readings very innacurate. I would say look into the 10A initial drain to see what's causing that. Once the interior lights fade out you shouldn't be seeing over about 1Amp drain in my findings. Of course your car might behave differently as it's a much newer model.

 

[Petrol Pete]

I have posted this on here a few times before , It's pretty good at explaining.

To view this content we will need your consent to set third party cookies.
For more detailed information, see our cookies page.

Accept third party cookies

 

[Glenzil]

I have posted this on here a few times before , It's pretty good at explaining.

To view this content we will need your consent to set third party cookies.
For more detailed information, see our cookies page.

Accept third party cookies

Ahh yes but mine isn’t a constant drain, it just takes ages to go to sleep. It would be interesting to find out if any other cars of my age and model have the same behaviour. It’s going in for a service next week so I’ll mention it to them and see what they say.

 

[Glenzil]

Ahh yes but mine isn’t a constant drain, it just takes ages to go to sleep. It would be interesting to find out if any other cars of my age and model have the same behaviour. It’s going in for a service next week so I’ll mention it to them and see what they say.

Actually that’s a good point, I will go thru the fuses and see if it’s one unit that is taking ages to go to sleep as that might be the problem.