NYC GLS450

Hi! I have a 2017 GLS450. I drove it yesterday with no problems, parked it at home last night. Come time to take my kids to school this morning, it wouldn't start. When I first got into the vehicle the console lit up, but there was no mechanical response when I pressed the start button. I then tried to jump the GLS with another car. After setting the cables and returning to the GLS cabin, I noticed that the console was no longer fully illuminated (only a few select dash icons were lit up, I forget which ones...) At this point, the car still wouldn't respond to a start button press. Trying to troubleshoot, I swapped my lighter gauge jumper cables for a heavier 2-gauge set. This time when I returned to the cabin, the console (and in fact the entire GLS) had no power whatsoever. No lights, no dash response, no power locks, no nuthin', and certainly no response to the start button press. At this point I had to figure out how to get my kids to school, so I manually locked the car and had to move on with my morning. Just to preempt a possible question, I used the lugs in the engine-compartment of the GLS to land my jumper cables, and also confirmed proper polarity on both ends of the cable set.

Any advice?

My hunch is a completely discharged battery is/was the problem. But I am puzzled by why the jumpers didn't at least give me some form of power to the GLS. Meanwhile, as I would like to put a multimeter on the battery to test it and, if necessary, change it, how on earth do I accomplish this when Mercedes has placed the battery compartment under a POWERED seat!! Real first-rate German engineering on that one...

I also think there could be some a blown fuse or fusible link at play here. Do any of you have guidance on which fuses to check? My understanding is that there are 3 fuse boxes, one under the hood, a second in the front interior cabin and a third under a rear seat (again, a POWERED seat...hopefully one that can be manually released...)

Any help or advice on how best to troubleshoot this would be immensely appreciated. Thanks for reading!

John CC

Did you try taking the button out and using the key like, well, a key? I'm not convinced the problem is the battery. Easy enough to test the voltage and the the under-hood jump point.

NYC GLS450

@John CC Thanks for offering a suggestion. I just watched a video on how easy it is to pull the button out, so I will give that and a keyed start a try later today. I will also put a meter on the lugs under the hood to see if I have any voltage.

That said, I still think there's an electrically-oriented issue going on here, given the complete lack of power. For example, merely opening the car door should trigger cabin lighting to come on, but that's not happening. Or if I depress the brake pedal, the tail lights should illuminate, but they don't. There is literally no sign of life at the vehicle. On testing voltage at the engine compartment charging points, in the absence of knowing how the car is wired, this could still be inconclusive should there be a fuse or fusible link in between those points and the battery itself. Still worth a check though, as you suggest.

I'm also remain really eager to learn how on earth to access the under-seat battery compartment when there is no vehicle power...

chassis

Replace the batteries. Main batt under the front pass seat and aux batt under the second row pass seat or in the right rear luggage area side trim panel.

The batts on this car are up to 7 years old depending on build date - past their useful lives. Modern German cars need 100% perfect batteries or unexplainable problems occur.

NYC GLS450

@chassis Thanks for the suggestion. Any tips on how to move the passenger front seat out of the way so that I can check/replace the main battery? Seems not doable without some form of power, but hoping there is an manual override...

chassis

I would use booster cables and connect to another vehicle or good battery to power the seat.

I would not check the battery, I would replace it.

John CC

That's foolish. How much additional time does it take to test the battery? Even if the battery is toast, you want to understand the problem, if only to ensure you don't cook the new battery.

The fact that attempting to jump it was unsuccessful points to a problem other than the battery.

wyatt88

Similar thing happened to my 2018 GLS. I was at remote location and no access to another car to jump. I did have one of those air compressor, battery charger devices that came from Costco. Plugged the charger into household current and connected jump wires as you described. No luck. Let the charger and connected jumper cables stay attached to the car for another hour and then was able to start the car.

NYC GLS450

UPDATE - PROBLEM SOLVED. When I got home from work, I went straight to working on the car. It was still effectively dead as a doornail. I took some time with a meter and checked all fuses and found no issues (worth doing this every once in a while anyway). I also had about 3.0-3.5VDC at the charging posts in the engine compartment, which told me that I didn't have a circuit interruption. I tried once again to jump the car. This time, when I made my final connection of the negative to the body of the source vehicle, I got a healthy spark and what appeared to be a noticeable electrical load on the source car (it literally dimmed for about a full second). At the same time, the GLS came completely back to life! This first thing I did, of course, was get the damned passenger seat out of the way of the battery compartment! Ran the car for a while last night and it's been running well throughout today, including a few stop / restarts during morning errands.

Thanks to anyone reviewing this and offering suggestions.

chassis

When you say the problem is solved, do you mean that you replaced both batteries?

NYC GLS450

@chassis Nope, just jumpstarted the car and it's been running fine through several start/stop cycles. No change to batteries. With that said, I do think I ought to get appropriate tools to evaluate the batteries and, likely, replace them. To your point, they are approaching 7 yrs. old and they aren't going to last forever.

John CC

Get the battery fully charged, then, most auto parts stores that sell batteries can test it for you. The best way is to take it out and bring it to them. Second best it to test from the battery terminals (under the seat). Last resort: test from the jump point, but, as you've learned, you don't always get the best connection that way.

007_e350

Lot of videos on youtube bro