CBelley

Vois à faire vérifier les petit modules électroniques sur les câbles proches des pôles. Ou carrément ta batterie ne répond pas aux specs lors de l'analyse du système.
Idéalement le faire scanner par quelqu'un qui a un Xentry spécifique MB te serait d'une grande aide.

Noxx

Went to the dealer and they weren't sure. They suggested that we replace the neg battery cable first which I did (myself). Still have the red light. Otherwise the car has been working fine for the past month.

calder-cay

Did you buy an exact replacement negative cable? It has a sensor in it that can go bad , so if you bought a "standard" cable, it won't have the sensor.

Mmr1

I bet a dealer would charge 550 for the job. Cable at FCP is 135.00.

Noxx

I bought a replacement cable from eBay (exact same part number, with the sensor).

Dealer wanted 750$ for the cable replacement. Mine was 80$ and it took 2 minutes.

Noxx

Still trying to find the issue. I'm thinking of replacing the alternator voltage regulator.

One thing I forgot to mention is that the battery light comes on as soon as I start the car (like 1-3 seconds after startup).

Mmr1

Why the regulator , I just did mine so I know about it. It took me a bit of testing to know mine was the regulator.
I’d think your Chinese cables may not work. I purchased eBay cables that were no good! . Do you have a load tester? Volt meter ? What is morning voltage and voltage after driving and while driving ? Do you have a good AGM charger ? Does it have an alternator tester built in?

Noxx

It's not Chinese, it's a used cable from another GLK. Yes I have a multimeter. I'm open to diagnostic ideas... If someone know what kind of ouput the cable sensor gives, I can check that as well.

Voltage is constant when I'm driving and idling. I logged constant 14.1V during a 3h drive and the battery remains at 12.6V after shutting down the engine. I don't have a load tester but I can buy one if needed.

Mmr1

All auto parts stores near me will test battery and alternator for free while you wait , they want to sell you parts . See what voltage drop is when starting it, and on first start of morning. I knew my regulator was bad because I had output but it wouldn’t charge my battery above 80% but a regular charger would .

habbyguy

The voltages you are seeing sound fine to me. The battery should be in that range with the car off. Unless it's dropping down to under 12.2 volts in a couple hours, it sounds like the charging system, and the battery are both fine. Modern cars don't try to charge the battery to 100% all the time, as that drastically shortens its lifespan, and is unnecessary.

Noxx

Little update, battery was dead after I left it alone for two weeks. So I have a new battery (again) and still have the error message. I now disconnect the battery when I leave the car parked for more than 3 days.

I replaced the neg cable again with a brand new one from MB. No change. My OBD scanner sees the battery voltage from one sensor (at 14V when running) while there is another sensor seeing 20V. Independant garage also said they saw a high voltage from a sensor so maybe it's the cause ? Where is the car taking it's voltage from ? I know that the battery is one and what else ? When I measure with a multimeter I get 14V everywhere I test.

Thanks

John CC

My guess is that you've masked the problem. Solve the battery drain and I bet the rest of the issues will go away.

Mmr1

Do you have an AGM battery and a charger for AGM ? Get one that also has a maintenance cycle and use it. With motor off hook up a meter and pull fuses one by one until you find the drain, you said one sensor is pulling 20v? The battery only supplies about 12.7v. A good charger is a Noco or CTEK , an inexpensive load tester for about 50$ would be helpful so you are on top of battery life and charge . Look for simple things first like door switch hood switch. Something probably isn’t shutting off. Even think about a jump box incase you get stuck somewhere. It’s no fun with battery issues and it’s getting cold. I just bought a jump box just for insurance.

Noxx

Yes I found that the drain seems to be coming from two fuses, ECU and car radio. At least for the first minute turning the car off, as my sensor can't measure for too long.

I don't think that my battery is AGM but it has the same specs as the original one. AFAIK the AGM is great for start-stop cars but mine isn't. I have a jump starter now always in the car.

Like I mentionned, my problem started last winter when my old battery died after 3 days of extreme cold. I tried to jump start the car a couple of time and since then I have the charging problem message. I suspect that jump starting with the Amazon jump box (pushing 15-16V) might have damaged something.

John CC

Consider this scenario: Something failed and drained the battery. With an older battery and the extreme cold it only took three days. Had you tried to start the car after only one day you would have found you had the charging problem indication then.

When checking for a parasitic draw, you have to give the systems in the car time to go to "sleep". This process can easily take 15 or 20 minutes. You also have to take into consideration that anything you do in the process of testing things will likely wake up some of the sleeping systems. Opening a door, for example, will invalidate any testing you're doing. Sometimes you can trip the door latch and the car will think the door is closed, but even that doesn't always work. If you have keyless go, and the key is in your pocket, the car is constantly monitoring the location of the key.

Does the sensor have a name? It is possible that there is a system in the car that uses 20 volts (and a source for 20 volts), although I expect a faulty sensor is more likely.

Mmr1

I replaced the Regulator on my alternator at 77000m , it was very worn out. Only about 140 at fcp euro. Much cheaper than an alternator . Yes you need to measure loss -drain after an hour or so.

Noxx

I bought an alternator regulator but haven't installed it so far, since I'm seeing 14V steady during driving (measured for a long period).

Ok, I will try to monitor the parasitic load for a longer time. I agree that 1-2 minutes might not be long enough. I bought a mini clamp amp meter for that purpose.

Thanks,

Noxx

Could be, but every month I leave for work for two weeks and leave my car parked at the airport. It did not show any issues before that 'incident'.

Mmr1

Two weeks is a long time to not get a charge , consider a solar panel. And a battery load tester to monitor charge . You might never get fully charged ! A low battery deteriorates- is ruined , from sulfation quickly. That’s why battery Maintainers are important for cars today. Cold weak batteries are the worst for your vehicle.

John CC

Understood. The question is, did the issue bring on the incident, or did the incident bring on the issue?

Is that rounding, or are you actually seeing 14.0 volts? 14.7 is closer to what you should expect. (Not that this is the issue with the battery drain.)

habbyguy

Make sure that clamp multi / ammeter is actually capable of measuring DC current through the clamp. The vast majority of clamp-on multi / ammeters do AC current with the clamp, and DC current only with the leads (which poses some significant difficulties for a car application, as most of them will blow an internal fuse any time the current exceeds "only" 10 amps (and that can happen a whole lotta ways with a modern car, by "accident").

FWIW, I've found that almost all modern cars run battery voltages in the 13.5 - 14.0 volt range during normal operation (plus or minus a couple tenths under extreme situations). Does the MB alternator REALLY supply 14.7 volts (which would be - IMHO - pretty hard on the battery)?

John CC

I'll have to pay closer attention to it. Bear in mind, that Mercedes specs AGM batteries for these cars, so maybe a slightly higher voltage is called for.

KTM530

You can easily monitor your battery/charging system strait from the dashboard will you are driving. Follow those steps: motor off, turn the key to pos 1, with the arrows on the steering scroll until the total odometer appears on the screen. Then press and hold the phone and ok until you have a menu displayed. Select the first item and press ok. Start the car, you now have live volts/amps data of your system. Positive amps means the alternator is delivering power, negative amps is the battery. High amps after starting the car is normal and will drop as your battery is charging. At start, mine is displaying 14.7v and as high as 30amps but droping to 14.1v after one minute and can go as low as 1.9amps after 10km. Great feature from MB.

Mmr1

The amp feature works, but the changes were very fast and hard to concentrate on. And how it responded back and forth in stop and go was hard to work out. On a steady drive it would be real good . It can help

Noxx

Unfortunately it's not possible, as soon as I start the car, I get the red battery warning message and can't aknoledge it.