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2016 E550 Coupe
Apparently relay "N" is staying On and keeping the ECU energized and toasty warm 24/7. (I assume it's N because the print says O but shows two O's and no N, so I'm assuming)
I measured current flow at the batt and it's all over the place, from maybe 2A to <15 as things turn On and Off in a never ending cycle. So I guess it thinks the eng is running? I dunno, but it's killing the batt.
I have no idea what is causing it to do this. Any thoughts?
Have you been able to scan for faults? Anything show up? If it is CAN, then those circuits being signaled would turn on and then off if the demand for them was not real. Is it possible the relay itself has failed in the ON position? Thus allowing juice to the other circuits ? Try replacing the relay to see if that fixes it.
Thanks WRC, but as usual, no faults or codes. Well, none that are real. The relay works fine, it's being commanded On. It turns Off if I unplug the smaller connector on the ECU. So I tried my old ECU, same thing. So no clue what it could be. The only thing I'm certain of is I'm super annoyed >: | and it killed my 18month old batt. Basically deep cycled it for who knows how long until the batt could no longer last overnight, which how I found out I had an issue.
I was hoping for a known issue and fix, but like my turbo issue, I tend to have problems nobody has heard of. So it looks like I'll need to rig this too. Tired of having to rig everything I own.
Yes it'll drain overnight and not start. I have not bought a new battery yet because it'll just ruin that one too. The first couple times it did it the voltage was anywhere from 9 to I think 4? If I forget to put it on charge, which I normally do the moment I get home, it'll be 7-9V in the AM. When on charge it'll be high 11's to 12.2, so it's toast. The current draw varies as I sit and watch it, which I can hear things turn on and off. A couple amps on up to over 15, which my meter won't read beyond. I'm not certain but I think "things" stop cycling on/off after some unknown time because I don't hear anything running the next day but that relay and the ECU are nice n warm 24/7, and a few other things are slightly warm.
I don't unplug the battery unless doing a reset or changing the battery. I did unplug it while checking current draw, to get the meter in there. I also let it sit a few days unplugged to see if it would fix it, and so it wouldn't drain. Now I plug it into a charger when I get home.
OBD scan via a variety of tools, including Autel & Xentry. Faults are always there in one form or another, but never anything important, and nothing new. 99.9% are U codes like elect steering, tranny, radio, headrest, just stupid stuff that all works. The remaining .1% I trigger myself on accident. Ironically, since this happened, I get far fewer U code faults. Many times I checked there were no codes, which was previously unheard of. This is no doubt a clue to the problem, but basically useless to me because I don't feel like tearing the car apart to figure out which of the fifty modules is the problem.
When I have time my plan is to tie the relay to a switch. I'd prefer to tie it to the ignition circuit, which I'll try, but I'd imagine it'll glitch out if I do that.
Thanks for the reply, and I'm open to any suggestions
These cars do NOT work right with stacks of faults.
The main VIP modules are somewhat fault tolerant to keep the vehicle driveable but performance takes a dive with busy CAN's.
When you run these cars with marginal voltage below 12V every module operates in the twilight-zone under "best efforts" law.... (Limp-Mode around the corner)
When running the voltage is ~14.7. The 12 was to describe the state of the battery after being deep cycled daily for who knows how long. All the engine controls seem to be responding at normal speed. No delays, hickups, or any of the weird stuff I experienced with the previous batt. With the old batt the Eco Start/Stop was the first thing to stop working, long before I had other issues, but Eco still works for whatever reason. Maybe my voltage is low but current is still good.
Xentry, says it's fine, as it always does. Kinda a waste of $ but I had to get it to at least check if it could see anything. Maybe I'm not looking in the right place but OBD has never worked for me and I doubt it will suddenly start to.
I've gone about a week now with no codes, excluding ones I triggered.
I installed the toggle switch to kill that relay and it stopped the drain. So now instead of <11.5V when I get off work, it's 11.8V. Of course it still won't charge up past 12.2 on the charger. Next stop, new battery, but might wait until after Xmas to avoid the traffic. Probably no parking anyway.
So you pulled relay, checked both relay & docking for corrosion, etc. and replaced. I do not have associated wiring diagram on hand, pull SAM and check connections below.
11-26-2022, 02:50 PM
