R129 parasitic battery drain

Shadychris

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67
Location
Cornwall
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SL320
!995 SL320 pre-facelift.

Sorry this is a lengthy one but wish to give as much info as possible about this headache of a problem

What I know:
Had a new Yuasa 5000 series battery fitted last November - charges fully to ~12.9V, battery indicator green.
With everything connected 'as standard', battery will drain to a point where it wont start after 3 - 4 days if not started and run for 20 mins or so every day.
Checked battery -ve terminal to ground with everything switched off (including boot light etc) and its leaking between 300 - 350 mA

Pulled all fuses and can measure about 20 - 40mA across fuses 8 & 9 in main fuse box under bonnet - likely combination of clock, stereo and IR remote control (odd that there is also another fuse (6) in boot for IR remote)
On fuse 6, in boot auxiliary fuse box I'm seeing about 300mA - so this seems to be the cause, as it seems to be generally accepted that the standby draw should be no more than about 40 - 50 mA.

What I've done as trouble shooting\elimination.
Checked alternator by running motor and checking at battery for any AC ripple voltage which would indicate bad diodes - nothing.
For good measure disconnected the dealer fitted retro factory alarm MBSS system under the bonnet
If I leave fuse 6 pulled out, the car will happily stand for a week or so without starting and still have more than 12.6V required to fire it up.
I've eliminated boot light - the switch works perfectly. To eliminate further, the central locking control\pump has been disconnected, as has the electric antenna, and for good measure the N26 ATA module (although that's on fuse 5) but I understand it interacts with the N54 IRCL unit on fuse 6)
However even with all that lot disconnected I still get ~300 mA across the fuse 6 terminals - the only thing still connected on fuse 6 is the IR control module N54, so it seems highly likely this is the culprit.

My problem\questions
My N54 module is not located in the boot above the CL pump and below the N26 ATA module - so I cant easily disconnect it. From the webetm Star Finder it appears that it is located deep under the dash on the nearside - and look to be a complete dashboard out job to access it :-( But the location on that photo is on a L\H drive car. So first question is will it still be on the nearside behind the passenger airbag - or does everything L\H drive model simply swap orientation to R\H drive?
Second question is about the module itself. If I can find it and identify that as the cause by disconnecting it and measuring across fuse 6 again, is it possible to simply get a s\h replacement N45 IRCL module and plug it in? Or is it in some way coded to the main ECM?
I have enough knowledge of electronics to know that my IR key fob has a set signal code, and that will programme itself to the IR receiver\control unit (as described in owners HB). But not sure if some ECM programme tweaking needs to be done to recognise a different IRCL control module??

Anybody have any experience of a) the exact location and how easy\difficult a job to get to it and b) whether a replacement module is just 'plug and play' ??

Thanks in advance!
 

alabbasi

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1606612900730.png

1) Turn your camera on your phone and put it in the boot and shut the lid. If you film the lights going out
2) disconnect the electric antenna
3) If you still have the problem, it's probably the module
 

BTB 500

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Sounds like you've looked into this pretty logically and systematically and your conclusions seem sound. One thing though ... a fully charged battery should provide 300 mAh for significantly more than the 3-4 days mentioned. My R129 has a 100 Ah one which would give 0.3A for almost 14 days before being fully discharged. So after 7 days it would still be at 50% charge ... does your car have a smaller battery? Also, was the car OK before i.e. this is something that's suddenly started happening?

On the module ... my guess is that the location would be the same for LHD & RHD models, and that a replacement one would need coding. But that is only a guess I'm afraid! Hope you manage to get to the bottom of it.
 
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Shadychris

Shadychris

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SL320
View attachment 105381

1) Turn your camera on your phone and put it in the boot and shut the lid. If you film the lights going out
2) disconnect the electric antenna
3) If you still have the problem, it's probably the module

View attachment 105381

1) Turn your camera on your phone and put it in the boot and shut the lid. If you film the lights going out
2) disconnect the electric antenna
3) If you still have the problem, it's probably the module
Thanks Al. Interestingly your (presumably US) model has exactly the same fuse box legends\assignations as my UK one.
Odd that my owners handbook correctly calls the boot a boot - whereas it seem both yours and my covers are labelled as 'trunk light' - sounds like an elephants headlamp ;-)

I will try a video in my boot, but pretty its not that as the current draw readings I get are with the boot light switch manually turned off. As stated in my post I've already disconnected the electric antenna - and all other modules on fuse 6 with exception of IRC which as yet I haven't located. I'll also try disconnecting the switch entirely as I guess there might be some internal current leakage going on there...

Thanks for taking the trouble to read and respond.

Chris
 

alabbasi

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I'm guessing that what they call the IR module is the vacuum pump that controls the locks, it should be in the (your) driver's side rear quarter panel, right above the battery.

It will be covered up in a rubberized box to dampen noise. You'll see a bunch of vacuume lines coming out if it
 
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Shadychris

Shadychris

Active Member
Joined
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Messages
67
Location
Cornwall
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SL320
Sounds like you've looked into this pretty logically and systematically and your conclusions seem sound. One thing though ... a fully charged battery should provide 300 mAh for significantly more than the 3-4 days mentioned. My R129 has a 100 Ah one which would give 0.3A for almost 14 days before being fully discharged. So after 7 days it would still be at 50% charge ... does your car have a smaller battery? Also, was the car OK before i.e. this is something that's suddenly started happening?

On the module ... my guess is that the location would be the same for LHD & RHD models, and that a replacement one would need coding. But that is only a guess I'm afraid! Hope you manage to get to the bottom of it.
Hi Bill,

Thanks for sanity checking my work so far.
Well spotted - you picked up on something that in hindsight I didn't quite describe correctly. On the one occasion where I did pull the battery out and bring it indoors to charge for 48 hours it stayed in a usable state with just starting and running for 10 mins every 3 or 4 days for, I think, nearly 3 weeks. What typically happens is that when the battery drops below 12.6V starting voltage is that I hook a charger up to the car for 4 - 5 hours just to put enough in to get it started again. I don't actually use the car that much and when I do a quick charge it's needing another top up after 3 - 4 days.

My battery is a 90Ah and agreed, my calculations give 12.5 days with a 300mA load. I'm afraid I first started to notice this about 2 - 3 weeks after I had bought the car. From the fact it had a new battery fitted just before last Xmas and was then sold on in March to the guy I bought it off in July , and I found the ATA module had been left disconnected in the boot, is making me think that this problem has gone unresolved for quite some time!

I burned the midnight oil last night and have discovered some rather uncomfortable news which answers my questions.... I'll post here for benefit of others:

It does appear that for cars with the N54 module behind the dash - it is found on the passenger side (regardless L\H or R\H drive) right up behind the airbag. Photo image is incorrect on EDM (as it also is for the boot modules which confuse the N26 ATA and IRCL modules) Quite some disassembly of dash required to get to it.

Re the N54 IRCL module itself I'm attaching some interesting and comprehensive info about that system here. It is indeed hard coded to the main ECM - a s\h unit from another vehicle will_ not_ just_work. A replacement would have to be ordered from MB with the correct hard coded number :-(
According to the manual the code is broken up into several sections and it is possible to recode the mechanical portion of the locking system number by MB with some kind of hand held manual tester. Presumably this is why they require you to turn up with the car when you buy a new key fob... Its not just a matter of synching it to the system by pressing the button twice (as I've seen suggested on another thread about buying a new key fob) but does require some authorisation on the N54. That's also in order to revoke lost or stolen key. The Descrip_IRC pdf explains all this in detail. It also indicate that the N54 sends\receives data to the X11/4 data connector - presumably how MB revoke\add new keys. So possibly the MB Star Diagnostics may pick up on a fault with the IRCL - but not sure it will on mine as everything 'works' OK with the system.

Think my next step will be to try and isolate the N54 connector lead at the boot fuse box and see if the current draw drops.
 

Attachments

  • Descrip_IRC.pdf
    493.4 KB · Views: 6
  • Functional_Descrip_Central_Locking.pdf
    568.2 KB · Views: 5
  • R&R_CoverBelowDash.pdf
    154.8 KB · Views: 4
  • R&R_IRCL.pdf
    90.5 KB · Views: 7
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Shadychris

Shadychris

Active Member
Joined
Aug 8, 2020
Messages
67
Location
Cornwall
Car
SL320
I'm guessing that what they call the IR module is the vacuum pump that controls the locks, it should be in the (your) driver's side rear quarter panel, right above the battery.

It will be covered up in a rubberized box to dampen noise. You'll see a bunch of vacuume lines coming out if it

Nope, the IRCL module N54 sends control signal to the M14/1 (vacuum pump) which I've already disconnected. It also sends signal to the flashing LEDS in the doors, and bi-directionally with the IR receiver and LED lamps in the mirror o\h console, and communicates with the ECM and the X11/4 data port. It seems to be at the heart of the system - including the immobiliser stuff in the ECM. Probably why the R129 Co quoted £1k plus to completely remove the immobiliser function.
 

alabbasi

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I just read your post. It sounds like you're about to have more fun than I could possibly bear.
 

Stratman

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Does you car have memory seats? I ask because 300mA is often what a faulty memory module draws.
 
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Shadychris

Shadychris

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Location
Cornwall
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SL320
Does you car have memory seats? I ask because 300mA is often what a faulty memory module draws.
Good shout - but no, unfortunately not..
 

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