Howdy y'all.

I've been having a problem the last few days with my radio shutting off at random. It turns off once or twice after I cold-start the car, and I've noticed it also turns off anytime the engine stops at a traffic light (with the ECO mode). If I lift my foot from the brake and restart the engine, the radio turns back on (displaying the Mercedes-Benz and COMAND logos, a fresh boot up). If I press the ECO button then the engine restarts and, ergo, so does the radio. It's really frustrating and rather annoying having my music or phone calls interrupted every time I come to a stop, or randomly as the car warms up.

What could cause this, and how can I fix it?

 

How old is your main battery?

I would try recharging the main battery. In my car, the absence of radio operation when starting the car signals a weakening main battery.

 

I have no idea, I have never replaced it since owning the car but I have only owned the vehicle since August 2022, so not long under my ownership. I will have it tested tomorrow.

Upon further inspection, however, it appears that when the radio shuts off, the "on" light on the center of the radio stack (in the center of the volume knob) flashes in a nonlinear fashion. I've taken a few videos and I'll try to upload them tomorrow morning when I wake up. It doesn't seem to have a real pattern, as it shuts off when I stop sometimes regardless of ECO status, and also turns on and off randomly whenever I'm driving at low speeds. It doesn't seem to do it much when I'm driving on the highway but it does do it here and there. Just with less frequency than at low speed. I'd almost suspect a bad ground if it weren't for the flashing "on" light but that makes me wonder if the radio unit is going bad.

 

I have added two videos here showing the issue: Read the description on the first to get more info.

 

Alright, so there’s got to be a bigger issue happening here. As I arrived at the mountain to do some skiing today, I got warning after warning on the dash. Blind spot, SRS, lane keep assist, a warning not to shift, every warning you can think of. Literally every light on my dash was on. The car wouldn’t shift out of drive. Eventually I got it in park, and then it wouldn’t turn off using Keyless go. I had to pop out the keyless go button and insert the key, which forced the car to shut off. Now as I go to leave the car has been sitting for a bit and it will restart, with no warnings, and then shout 10 seconds later I get the lot of them.

I’m now stranded at the ****ing ski hill and I am supposed to work tonight - all I can think of is that something somewhere is loose, but I don’t know where to look. Anyone have any ideas?

 

Surely the ski hill has a security vehicle with a battery charger... Almost certain this is a power problem, not a mechanical one.

 

You think all this could really be caused just by a low battery?? I mean the car starts right up, it just throws every warning under the sun after it does. Could the auxiliary battery have anything to do with this?

 

I towed the vehicle home yesterday and started digging. I checked on the SAM units and the rear spare wheel well, and found no evidence of water or moisture in any of those locations. I should note that I do keep my skis in the back of my car but they’re in a ski bag, so some condensation can escape but they’re not dripping all over the place. But again even as such I found no moisture near those units that I could see without removing them from the car.

My next thought was perhaps a bad cell on the battery, so I yanked both the main and rear auxiliary batteries and had them tested. The auxiliary battery tested fine, and the main one said it was good but needed a charge. I cleared all the codes I was getting from the car with my two-bit Bluetooth code reader and now when I start the car I’m only getting pre-safe and traction control system warnings, though I’m sure that pre-safe can’t operate if the traction control isn’t working.

I think I’m going to take it for a drive and then test the battery again to see if it tells me it’s good but needs a charge - if that’s the case, I’ll replace it and hope that fixes it, though I’m not sure as the car has thrown a bunch of warnings like this once before, which I fixed by pulling over and restarting the car. I actually made a post about it here but nobody responded.

The most compelling evidence I have right now of s battery/power issue is that when I start the car the COMAND screen turns on, and if I slowly turn the wheel, it’s fine. But if I make a quick turn of the wheel, the screen does a hard-reboot. With the power steering being electric all I can think is that the issue is a bad cell in the battery leaving the car with enough voltage to think everything is good in the hood, but not enough voltage to actually run the necessary functions all at once.

Anyone else had a similar experience, or have thoughts on my harebrained ideas?

 

I have a S212 (2015) and my wife a W166 and I've seen some strange behavior due to low battery issues. On the S212 I had the typical "ECO mode doesn't work" issue, so I started putting the car on a trickle charger. Eventually I had an issue where none of the driver's side door switches would work, which required charging both the main and aux batteries and a hard reset by disconnecting both batteries. My batteries were original and at about 6 years of age. I replaced the main battery and haven't had an electrical issue since.

On the W166 (2018), we experienced the issue where the dash displayed a number of warning messages for blind spot inoperable, SRS inoperable, etc (basically all the safety systems). We were able to drive it a short distance home where I put the car on the trickle charger. If I recall correctly, this was around the December holidays and my wife was making numerous short trips with the car and I assume the battery was in a degraded state. It's been over a year and hasn't happened again.

My advice is to start with the main battery, and if it is more than 4 years old then just replace it versus nursing it along with a charger.

 

I think we've solved it. I had the battery tested and then reinstalled it once it was fully charged. I then drove the car down to the parts store and got no warning messages, no lights, it was as good as new except for the continuing radio shutdown issue that has persisted since I started this thread.

I had them test the battery again to see if the tester showed that the battery needed charging, which it did not. I then had them test the alternator and found that the diodes were good, but the voltage regulator was bad. This would track with all of the issues I'm experiencing, as spinning the wheel with the EPS would cause a voltage drop that the regulator can't reconcile in a short enough period of time. The battery was only as old as 6/20, so I don't suspect it to be the culprit unless it had some kind of catastrophic damage, like freezing while discharged, which can't have happened since I've owned the car. I think I'm in the clear here, so I intend to keep driving until the new alternator arrives (solely because I don't have another vehicle to operate in the meantime, and I work for a living).

I appreciate everyone's help - hopefully this fixes it, either way I'll try to remember to return to this thread so that those with this issue in the future can benefit from my learning experience. Hi, future people!

 

I had charging problems on my pickup truck, found I could drive up to about an hour between manually recharging the batteries (dual battery diesel truck). Basically I put my NOCO Genius 10 on it each evening and didn't go over 50 miles.

I'm curious how a parts store could test the "smart" LIN bus controlled regulator on a Mercedes?

 

Basically they hook the tester to it while the vehicle is at an idle and add a load (in this case, it draws current to heat a few electric coils in the tester). If the alternator reacts immediately to the voltage drop created by the sudden load, and supplies adequate voltage, both the alternator and voltage reg are good. If the car can’t provide the necessary voltage, the diodes are bad. If the car provides the necessary voltage but doesn’t do so at a consistent rate, or doesn’t react fast enough to the load, the voltage regulator is bad.

This wasn’t a bench test, they test it right in the car and so they can use the rest of the electrical system (namely the battery) in the car to determine how the alternator reacts.

 

find S-Pri....'s extensive set of tests of the Mercedes smart alternator system. its way too complicated to test that way.

 

I know about the smart charging system but it shouldn’t matter at an idle. It’s an alternator not an electrical engineering degree, why can’t you test it that way? Also, I can’t find what you’re talking about.

 

if the ECM thinks the battery is mostly charged, it tells the alternator to drop its output to 12.6 volts. The ECM monitors the battery charge state via a shunt current detector thats on the negative terminal, and by measuring the battery voltage....

 

Yes but that would test the diodes, not the voltage regulator, correct?

And again, that’s if the battery is charged. By adding a heavy current draw to the battery, it discharges, which triggers the alternator to begin charging again, yes?

When tested, mine showed ~14V, I don’t remember what it showed for current.

 

When the engine stops, what does the car read for battery voltage?

 

It reads ~12.6V as it should. The alternator is charging, just not regulating the current properly.

Today I removed the alternator and did an exploratory disassembly of the back. Removing the voltage regulator, I discovered significant scoring on the alternator shaft and equally inverse wear on the inner lobe on the voltage regulator. Photos below.

 

It appears this was, in fact, the problem. I have replaced the alternator with another of similar stature and found that the problem is decreased but not eliminated. Basically, the part number on the alternator I got and the part number on the alternator I ordered were not the same, and as a result, I had to swap the old voltage regulator to the new alternator. This reduced the problem significantly as the new alternator does not have grooves deeper than the Grand Canyon in the stator shaft.

I will be starting another thread (or maybe it's best done here?) to determine whether I can use the new voltage regulator in the new alternator and whether that will work, or if they're not cross-compatible and if I will have to order yet another alternator since I can't find the proper voltage regulator.

As always, will update further when I have totally rectified the issue.

 

This rotor looks wasted for some reasons. OEM carbon brushes are softer than the also soft copper. This is a carefully matched pair, like the brake pads/discs.

FYI: The current is *not* regulated, only the voltage is regulated.
(However current is measured internally by a shunt resistor so the ALT can protect against hazardous short-circuit conditions).

 

Yeah the stator shaft looks wasted because it’s original to the car with 206k miles on it. The new alternator is an OEM Valeo with 37k on it, and the brushes are fully one inch longer and the grooving is minimal if noticeable at all on the stator shaft.

I’m surprised it’s held on this long, honestly.

 

Howdy.

In following with my other thread about the cross-compatibility of the voltage regulators, I have now replaced the alternator and voltage regulator entirely with parts off a very low-mileage car of similar spec. I have also replaced the battery with a new, 850 CCA AGM battery. The car continues to run without incident, no more christmas tree of lights on the dash or warnings. But the radio (the original complaint) CONTINUES to be inoperative intermittently. As best as I can deduce whenever there is a voltage drop of significance, such as spinning the steering wheel very quickly, the radio dies out. On cold starts, the radio usually does not turn on for 30mins or more, well after the car comes to operating temperature.

What the hell else could it possibly be? The voltage regulator and alternator have 37k on them off a similar car, so I assume they must be good though I have not tested them. The battery is brand new, dated 12/22 (the old one tested fine as well, dated 06/18, but I replaced anyway because I couldn't think of what else it could be).

Bad ground somewhere? I'm dying to get this sorted. It is driving me insane that the radio only works sometimes, and since the power steering tends to take the radio out, parallel parking is a ****ing fantastic experience, since you go to look at the backup camera and it dies out.

 

Based on reading your thread, i would guess you have an issue with power that caused SAM to shut off consumers and crashes your COMAND NTG when you exert a hard load with electric steering rack.

For some reason you've replaced Battery and ALT but the same issue continues...



> Russian Dolls:
Many basic factors can gang up to help create a more complex issue.

• bad NTG module,
• bad unsoldered R-SAM,
• painted GND reference,
• soft-crashed F-SAM/ECU,
• oily wiring harness,
• noisy harness path,
• bad Hyundai sensor,
• toasted Prefuse path,
• batteries collection,
• loose connection,
• . ~ your own issue ~ .

All that amazing chaos underwrapped without any direct code!! 👏

What's missing are troubleshooting steps to pin point what is going wrong.

> Read the voltage display on maintenance menu to see what happens to Batt. VOLTAGE and CURRENT when the ECU is controlling the ALT after initiating the 12.6V float cycle.

> Scan you car to retrieve ALL listed faults.

> Disconnect ALT control lead to instantly get a reliable power source. See if stable car voltage relieves NTG issue.

 

a marginal ground somewhere in the critical path would do this... get a long (15-20 ft?) piece of insulated copper wire, gauge doesn't matter, and a multimeter set for DC Volts, low voltage range (like reading single digit volts). connect one end of the wire directly to the main battery negative terminal. go around with a volt meter set for millivolts, and measure the difference between the far end of that wire and other ground points when the engine is running, and a friend is twisting the steering back and forth. test at the rear SAM, and the ALT battery especially.

 

Cali, you are the kind of gigachad MBWorld power user I have been hoping would find my threads. Lol. I’ll be following through on the rest of this list as well as the most recent post above me, but I have checked the voltage with the maintenance menu and I can see that the current and voltage are both positive and charging, respectively. There is a pretty heft dive in current when I yoink the wheel super hard but I assume that’s to be expected…?


I did do some code reading back when I was getting the Rockefeller Christmas Tree on my dash, but I don’t have a Mercedes code reader, I just have regular old code readers, so the code I was getting was a “data bus, vehicle dynamics control module - no communication” code (U0122) code but I was pretty sure that the problem lay beyond that and I just couldn’t see it because I didn’t have the spicy code reader. That code also triggered a CEL which I’m no longer seeing when this occurs. Is that still worth chasing?

My gut is screaming loose ground, but there are so many I don’t know where to start. I also don’t know where to start with half of the things you identified - soft crashed front SAM? Hyundai sensor? I don’t know how to identify these problems... Is there a thread that outlines those steps?

Thanks for all the info - I’ll be putting it to
good use as the time comes to me to do so.