Anyone have a guide as to how to remove the rear SAM/fuse box behind the passenger seat? I have an aftermarket audio amp down there that I think is grounded to the negative aux battery lead that is causing the car to throw a code.

 

See attached .pdf from WIS

What codes are you getting?

 

Thanks so much. I am wrestling with a B21DE7 code that keeps coming up "The Relay 'Additional Battery' Has a Malfunction. The Actuator is Blocked." The only real symptom I have from this (from what I can tell) is that the ECO Stop/Stop no longer works (the button lights up on start up, along with a yellow ECO in the cluster, but then the button light goes off and the ECO in the cluster goes away and cannot be activated again) and that the aux battery seems to be draining quite quickly (I replaced it with a MB OEM about 2 months ago as a first step).

There's this TSB which suggests grounding to the battery (and, I assume, the same chassis point where the battery is grounded) can create a similar fault - https://static.nhtsa.gov/odi/tsbs/20...63569-2280.pdf).

I had a small aftermarket Class D (AudioControl) amp installed by a shop to power up the rear speakers. I can't follow the wiring, but it looks like power is being run through a 30A fused line from the aux battery to the amp and then ground to the same chassis point where the aux battery grounds. I cleared codes and pulled the amp fuse to see if that would make a difference - it did not.

I may have the shop pull the amp to see if that has any effect.

Any thoughts?

 

Sounds like you’ve replaced the AUX battery but, I would also test the Aux battery by conductance or load testing, not just voltage. XENTRY will show AUX battery condition too. Voltage isn’t necessarily a good gauge of how the battery is performing. You might want to also charge that Aux directly.
see here for some Aux battery tips.
https://mbworld.org/forums/sl-class-...t-guide-5.html

It’s hard to tell what went wrong with the aftermarket stereo installation. Sometimes even grounding a positive wire connected to the SAM can scramble its normal functions.
But those symptoms you describe are typically indicative of a weak Aux battery. Did this all start immediately after the installation or did it start a bit later?

 

Thanks again. Issues started very shortly after the stereo install (the amp is installed next to the rear SAM which leads me to believe this has to be more than coincidence - only other change was adding a RoadTop CarPlay unit).

I pulled my aux battery and fully charged it - that took care of the "Aux Battery Malfunction" message in the dash, but I still have the ECO button issue.

I also used my aftermarket MB scanner to pull voltages and battery condition. Aux battery is showing 12.7V on the scanner and 12.9V on the multimeter (but to your point, I have not load tested it). The main battery is showing 12V on the scanner and 12.2V on the multimeter. I pulled the main battery and had it tested (report was "GOOD"), but part of me wonders if perhaps the main battery is weak as well and creating some gremlins. Reason I say this is reading up on the RoadTop CarPlay unit, RoadTop says that if you charge the car, the unit stays active and will draw power. Because I don't drive much, I kept the main battery on a tender. I wonder if that was waking up the RoadTop unit, causing the amp to turn on, and then drawing power from the aux battery (thus draining it). Before the "Aux Battery Malfunction" indicator in the cluster, the only symptom was the ECO issue (noted above) which I think could be related to a weak main battery (contrast -aux battery drained caused the DISTRONIC to stop working and the brake hold to stop working).

I'm riffing a bit here. Not sure if the next step should be to replace the main battery or to perhaps pull the amp.

 

I should add that the 12.2V on the main battery was after charging it.

 

Interesting, since it started shortly after, we can pretty much guess that it wasn’t an instant failure. It took some time to manifest.
To me, if I had to make my best “ Internet Guess”. It sounds like a power/charging issue relating to the Aux battery G1/7 circuit. The charging circuit on that Aux battery is delicate. If it was arc-shorted, it may have prevented the G1/7 battery from charging. But since you’re not driving the car too much, that points to the possibility of an excessive voltage draw, especially if the amp is wired to that circuit as you mentioned below. It’s also possible you have more than one issue.

The ECO function is typically tied to the Aux battery G1/7, not main battery G1/4. So I think it’s related to that G1/7 circuit.
see attached PDF’s in post #105:
https://mbworld.org/forums/sl-class-...ml#post8606575

As mentioned, the ECO function failures are usually attributed to Aux battery G1/7 or circuit. Of course that is as long as you have confidence the main battery test was done correctly….

If they wired the amp directly to that Aux battery or it’s related circuitry, then that is a very strong possibility! I would have thought a competent installer would wire an amp to the main battery G1/4 circuit.

More likely Aux battery….

I would definitely trace where that amp is getting power from…..
if it is the Aux battery I would route it to the main battery G1/4 circuit. I would think an amp has quite a bit of draw. And if it’s always on, or getting intermittently powered on, this would be a prime suspect. It would explain the issues with ECO function and discharge of the Aux G1/7 battery.

Though more of an outside chance, You may also have to clear the codes properly in XENTRY. There may be other codes not visible to your scanner, that until cleared, are preventing some functions from working properly. but I would definitely start by finding where that amp is getting power from….

Good Luck

 

This is awesome. Thank you. Any idea how you would identify those circuits in the rear SAM area? Will try that first. If no dice, then a main battery and then off to get XENTRYfied!

 

Took it to the stereo shop. Some interesting results:

1) The amp was connected directly to the aux battery relay for power. The ground was connected to the same chassis Point the aux battery was grounded.

2) The shop agreed this was not the way to do things (they suggested they were just following the instructions from the rear speaker tutorial on here, but that just says get power from the SAM, not wire to the relay).

3) The aux battery relay appears to now be busted and constantly stuck closed (meaning that it’s connected to the charging circuit when the car is running). Voltage drops from 14 something to 11 something when the relay tries to disengage but it can’t fully. That seems to be what is causing the code.

3) Shop hooked up their super duper fancy SnapOn scanner, pulled the same code (along with a sun sensor code and an interior temp sensor code - no idea what those are about) and cleared them. No dice (which makes sense since the relay seems screwed).

4) Relay is part A 000 982 2023. Special order from local MB dealer. I ordered it for $350.

Stay tuned if the replacement relay does the trick.

 

I think you found your issue…
That’s a very common failure point in the G1/7 Aux battery circuit. It’s fairly delicate to power surges. You can blow that module/relay out from a bad jumpstart too. Definitely not the best place to connect an amp ☹️
Btw. That code you initially mentioned (at least a variation on XENTRY) points to that relay being the issue too.

Good Luck!

 

You are a good dude. Thanks for all of the help. I will report back once I get the module to see if that fixes the issue. Seems like the amp pulled too much power through the relay and busted the contacts. I may try to take the old relay apart once the dust settles just to see what kind of failure we were looking at.

Also - $380 for a ****ing relay!

Do you happen to know if WIS has any specifics on which lead attaches to which contact on the relay? I want to make sure the shop doesn't wire it in backwards and put us right back where we started . . .

 

I’m not in my shop so don’t have access to WIS right now, But remember the battery goes to the outer terminal. (red circle)
I can double check tomorrow….

 

Thank you again. I got nothing but time while I wait for the magic parts fairy to deliver my relay, so if you wouldn't mind checking, I would be happy to send you lots of good karma.

 

WIS section attached on that "additional battery relay" shows images, Note the smaller cable is on the outside terminal (that relay is designated as K114)
Hopefully that helps some....
Wiring diagram may not be much help because it shows K114 connections, but not necessarily in order as they appear on the relay itself. I've included it anyways in the attachments.

Good Luck!

 

Decided to install the relay myself. Disconnected both batteries and replaced the unit. Cleared codes, fired her back up, and as soon as the ECO message in the dash disappeared it threw the same code. So $380 later and I am back to where I started.

Sort of stumped as to what to do next . . .

 

That’s disappointing, I would double check ALL the connections and grounds to/from the Aux battery. Make sure everything is tight and clean contact points. Charge both batteries fully. Also make sure you resistance test both batteries.
XENTRY will be able to check the operation of the rear SAM. On the surface, it definitely pointed to something going on with the relay. But electrical issues can be like playing whack-a-mole. Especially if someone has been tampering with the electrical system.

Something in series with that relay such as the SAM could cause issues, but I always try to start with the basics. I’m assuming you disconnected the Amp?

 

Amp is disconnected (specifically, removed). I checked voltages and what I am getting in the scanner is the same as the multimeter, so I don't think it's an issue with the battery sensor.

When I test the relay with the multimeter, looks like both leads are showing 12.7V - same as the aux battery (and whether the car is running or not).

Main battery shows 14.7V when running and 12.5V when not.

Next stop may be a shop with XENTRY to try to figure out what's going on. I need to do a resistance test of both batteries as well.

 

Does everything on the car work properly, Including ECO function? (now)

 

Everything works other than the ECO function. Also, check out these pictures from the old relay - the thing was mangled:

 

ECO is the only thing that isn't working. And according to my scanner, the car is still throwing the same code (which, weirdly, is a variation on the code that you noted in your prior post and there doesn't seem to be much info on). Any sort of coding that needs to be done when replacing the relay?

 

No. But be sure to check your batteries (resistance) …

That’s a mess, and bad news. Someone replaced that screw. They either stripped it, got it hot, or just decided they needed a longer terminal. That some janky $h!t for a tech to pull on such a nice $150k car. You needed to replace that relay anyways. So that was a win… Sorry that happened to you.
Bad news, because something may have gotten shorted, no way to tell now. Check all your fuses too. Hopefully it’s something minor. 75% of the time it is. 😕

Xentry will show charging cycles on the front and rear SAM’s so it will make diagnostics of those units possible. Also will show ECO operating status and voltage conditions of that Aux battery circuit.
something like this below:

 

Yeah - this was a real hack job and I suspect someone at the stereo shop did it. Going to have to take it to a shop with XENTRY to be able to sort this out now. Will get the batteries tested and find a shop. Stay tuned.

 

Tested both batteries. Aux battery was good with 100% SOC and SOH (measuring 9.6 mOhms). Main battery was low, but showed good needing recharge.

I pulled the aux battery and measured the voltage at the aux battery relay - on the inner terminal, it's showing 12.5V (presumably from the main battery). Outer terminal (where the aux battery connects) shows 1.25V. I am assuming if the relay was closed, both sides would show 12.5 V, so it seems like the relay is closed. Should voltage be leaking like that if the relay is closed?

Still working on getting time with a shop that has XENTRY.

 

That is correct , relay should be closed when Aux battery is fully charged (or within spec), it should open when Aux battery is low (and I believe ignition is on) allowing for charge from alternator.

Presumably that is not happening, that’s why it’s throwing a code.

 

I think that's right. Car starts up, it's sending a signal to close the relay (disconnect aux battery from the main charging loop), and the relay won't close. That condition is causing ECO mode to become disabled. Think I am at a dead end absent diagnostics now.