W169 Parasitic battery drain

[Tombob]

I've posted on this previously but am hoping for more clues.
My partners 2006 A170 Elegance is still destroying batteries - I don't know if my money or my patience will run out first.

I've unplugged the Bluetooth phone thingy under the passenger seat and replaced the Audio20 (which was fried) with a Panasonic double din head unit unit with wireless Carplay. That lowered the drain substantially and the sound system works fine, so that was at least part of it.

I've just spent AUD1,100 with a mechanic who specialises in parasitic battery drain. He replaced the battery and the ignition relay, which was "hot" and "stuck on". According to the invoice this lowered the drain from 250ma to 120ma but he advises this is still too high and says "The next stage would require the Ignition module and the junction box to be removed and tested".
The shining turd is he returned the car with the Climate Control AC not working (screen and LEDs look right but doesn't blow cold) so I don't know if he dislodged or broke something but I fear sending it back without knowing more ... despite today's forecast being 36C.

We inherited the car from my parents in law who had it from new. It came to me with an enormous list of issues I've now mostly fixed. At under 90,000km I've replaced the entire front suspension including the steering rack, 2 "bouncing" door locks, AC compressor, broken door barrel (door key spun uselessly), remotes wouldn't lock or unlock (but central door lock switch worked).
My neighbour re-soldered the IR door receiver dry solder joints so now the doors lock/unlock with IR but still no RF. Re-synching the keys didn't work so I paid the Merc dealer to run diagnostics but they found nothing to identify the RF issue. For AUD300 they confirmed the keys worked but that's about it.

In the 5000ks since we've owned it the drive shafts have also failed. A mechanic friend suggests a "do not revive" sign.

I suspect at some time there was a significant insult to the electrical system and that might have spiked various things but that's only speculation and nothing definitive is showing on any mechanics' scanners.

Thoughts?

 

[Blobcat]

You can with a multimeter check for voltage drop across fuses when the car is off - with that info you can then ascertain what is causing the drain.

 

[bembo449]

clamp meter and pull fuses

 

[Tombob]

Thanks bembo and blobcat.

I tried with a multimeter but the readings kept changing over time as computer electrical systems changed state or shutdown over time - it was much simpler in the analogue days where you could diagnose anything electrical with a bulb and some wire.

The guys who last looked used an oscilloscope to plotted the drain over an hour or more after shutdown - apparently some things stay switched on (e.g. signal receiver for remote keys) and other things turn on and off periodically. The battery still starts after 10 days of little use so the parasite has receded behind other priorities. Other good news is I removed the carpet to view the relays and found they'd accidentally unplugged what appears to be a sensor lead running along the tunnel to the AC unit. I plugged it back and the AC now works.

I'll post again on the issue if I discover the root cause of the drain.

 

[Tombob]

Grrrr..
So speaking of "drains" I now see the passenger floor is is sopping wet after a recent downpour.

In the 10 years we've owned the car we've never seen this so I can only assume the guys who removed the carpet to work on the relay plate disturbed a drain line from the plenum chamber. I'll pull the pollen filter and check the drain there but it would be an extraordinary coincidence if this happened to block just now.
Any advice on what they might have disturbed when accessing the relay plate (or is this just an extraordinary coincidence)?

 

[Flyinspanner]

Check that the windows all shut properly - may need resetting after recent battery disconnections?
Pollen filter blockage?
scuttle drains under the windscreen.

 

[Tombob]

This car has more drama than Neighbours.
Yes, the scuttle drains were blocked so I'll put that down to my lazy stupidity. Not the first time, not likely the last.

On the battery drain, another mechanic was suggested so I took it to him. He immediately unplugged the audio head unit to remove it from the list of suspects but confirmed the battery was still draining.

He was bewildered by the receipts from the previous diagnostics. Based on his experience he strongly believed the SAM was damaged by previous water ingress so he replaced it with a second-hand unit. He said this is not an uncommon issue with Mercedes.
He has left the head-unit unplugged and returned the car to me, so we can confirm the battery stays charged. So far so good but does anyone know how long a new and charged battery should remain viable if I just leave the car unused?

Also, how come the Mercedes dealer didn't detect the SAM as faulty (if this was the issue)? Surely this would have shown on their factory diagnostics?

Lastly, the RF for the remote central locking has never worked while we've had the car and is still not working (new batteries in both remotes). I had hoped this was also caused by a failing SAM - I've been relying on the IR receiver in the door handle ... which I've previously repaired myself for dry solder joints.
Anyone with further thoughts on the RF?

 

[Tombob]

It's only taken 5 years of burning batteries but I think the parasite has finally gone. It seem the definitive fix was replacing the SAM.
The mechanic was already convinced of this as his clamp meter showed the drastic drop in idle consumption, but more evidence is the car starts without issue after sitting unused for about 2 weeks. I'll post again in a few more weeks but I think this is it.

My research shows there are SAM repair specialists but on that the mechanic rolled his eyes, which I interpreted as he's had bad experiences. I'm curious if this is the universal opinion. I'm also still curious how Mercedes couldn't identify anything with factory diagnostic tools.

The RF for the remotes is still not working (so this issue wasn't the SAM) but the door handle mounted IR is sufficient until I regain my trust in Mercedes and delve further.

Last thing: Proving what we've all been told about keeping the plenum chamber drain clean, you can clearly see the dirt line on the pollen filter, witnessing the high tide mark.

 

[peterws1957]

It's only taken 5 years of burning batteries but I think the parasite has finally gone. It seem the definitive fix was replacing the SAM.
The mechanic was already convinced of this as his clamp meter showed the drastic drop in idle consumption, but more evidence is the car starts without issue after sitting unused for about 2 weeks. I'll post again in a few more weeks but I think this is it.

My research shows there are SAM repair specialists but on that the mechanic rolled his eyes, which I interpreted as he's had bad experiences. I'm curious if this is the universal opinion. I'm also still curious how Mercedes couldn't identify anything with factory diagnostic tools.

The RF for the remotes is still not working (so this issue wasn't the SAM) but the door handle mounted IR is sufficient until I regain my trust in Mercedes and delve further.

Last thing: Proving what we've all been told about keeping the plenum chamber drain clean, you can clearly see the dirt line on the pollen filter, witnessing the high tide mark. View attachment 87580

Glad you seem to have it sorted. Battery drains and leaks can be difficult to identify but MB's seem to have these common issues. I'm also surprised the MB dealer couldn't identify the problem, but the cost of them doing so and then rectifying would probably have been eye watering. SAM's can be repaired depending on the fault but it seems to be hit and miss whether these repairs last and/or work when connected to the car as opposed to bench testing.
If you're going to leave the vehicle standing use a battery maintainer like CTEK or something similar. MB's are the only cars I have had that needed this to be done.