EIS Circuit 15.

steveskeggy

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S55 AMG
Hi.
After much work/illness/head scratching, I have finally rebuilt the engine on my S55 AMG, Overhauled the two heads, new timing chain, new oil pump and drive chain, new water pump, other stuff I cant remember.
The engine is now running well, and I can (sort of) move the car.
The problem is, that I can only start the car with the keyless go on top of the gear selector, the EIS doesnt work properly.
It moves the steering wheel when I put the key in, but does not illuminate the dash, and does not start the engine.
Also, the gearbox will not release when I press the brake pedal, it will only release if I smack it with a rubber mallet!
It seems the brake lights dont work, the left one is on all the time the ignition is on, but the central does not come on, neither does the right (although the bulb may be blown).
The only other thing that doesnt work is the courtesy light when I open the doors, they all work with the switch front and rear.
I am using an Autel Maxidas, and there are a lot of faults that mention circuit 15 and one which reports 15a.
I have searched the internet, and tried to make head or tail of the Mercedes wiring diagrams, but I cannot find much information about this elusive circuit 15
I have a feeling that all of the faults are connected, perhaps not the courtesy lights, but the brake lights and gear selection certainly.
There is no brake fluid in the system at the moment, and the pads need refitting, but only after the discs have been skimmed as they are rather rusty after 2 years of no use.
All other electrical systems work.
I could live without the EIS as I always use keyless go, but I dont like the idea, and I need it to reset the throttle to the new 80mm body.
I have tried fuse 78, which seems fine.
The engine ECU has been serviced and repaired after water got into the plug and a few of the pins broke.
There are quite a few fault codes on the reader, but these can be ignored as they are for the suspension, which has been swapped for coilover, and the sound system, which has been swapped for an Android system with seperate amplifiers.
Can anyone suggest anything that I could try? I cannot get it to the dealer because it is not roadworthy yet, and has no tax, Mot or insurance on it, and the nearest dealer is 30 miles away.
And if someone can explain in plain English with no technobabble what the hell circuit 15 is, where it gets its power from, which relays/fuses could be faulty, I would appreciate it.
Thanks
Steve
 

bob6600

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Brake light switch?
 

grober

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circuit 30 is battery voltage positive - continuous
circuit 31 is battery voltage negative - continuous
circuit 15 is switched positive
circuit 15R is ignition switch in posn 1, 2, 3
circuit 15X is ignition switch in posn 2
This might have something related to your keyless go/ ignition switch meaning certain modules are permantly powered giving the impression there's power there----- BUT not for certain ignition switch powered modules?
W220 S-Class Encyclopedia
 
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steveskeggy

steveskeggy

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Thanks for the replies.
Bit more information.
The Maxidas reports this:
No OBD fault codes

In live data:
Power supply 12.3v
EZS Initialised - yes
Transport protection detatched - yes
EZS Activated - yes
EZS Personalized - yes
Key Inserted - yes
Recieve Start Message of Key - yes
Key Data Are Being Entered - yes
Coil Supply for Transmitter Switched off - No
Start Enable - Yes
Key in Position H0 - yes
Current Key or Track - 5
Version of Control Module EZS - Replacement
Shift Lock - Inactive
Open Circuit 15R - Off
Open Circuit 15 - Off

Then serial numbers and test counter.

From this data, and from the replies, I would rightly or wrongly think that the EIS is working OK on the data side, but is not recieving a voltage feed to send power to the rest of the system, and if I am guessing right, the power should come from circuit 15?
I have looked at fuse 78, and it looks not to be blown, however I did not check if there was any voltage to it.
I also checked the rear junction box/prefuse in the boot/trunk, all looks well there.
I looked for the other junction box in the footwell on the left side front, there was not one there.

The keyless go is working mainly fine, although it doesnt seem to care if the brake pedal is pressed or not to start the engine, which it sometimes does not, it just parks the steering column and switches off. The doors lock and unlock fine.
I will look further to see if I can find the other Junction box, it should have one according to EPC, and check if there is voltage at fuse 78.

Thanks
Steve.
 
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steveskeggy

steveskeggy

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S55 AMG
Further to yesterdays post.
I am ignoring fuse 78, as it also supplies to the windscreen wipers and steering column movement, which both work.
I see from WIS that the EIS has a cable for the shift lock, this would explain why the selector will not move.
I still think there is a power fault to the EIS, either that or the EIS is faulty, but I cant figure out how it could go faulty when it has just been stood with no power running through it.
I got the car running before the ECU packed up, and it was the same then as it is now, it has not worked since the car was stood up.
I have included two pdf files, to suppliment the normal fuse diagrams (Blatantly ripped from w220.ee and edited with word).
 

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Alex

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You say you had a new ECU. Was it programmed in for the key?

When the key is inserted, your EIS, ECU and (from memory) CGW do a handshake. Don’t know the capabilities of your Autel but in my Snap On scanner I am able to log into the EIS and monitor its status as I insert the key (it changes to Yes). You should try that before you write off the EIS.

Other than that it sounds like you’ve lost your ignition feed somewhere. Could be quite simple - you connect it and all powers up. I take it your battery is fully charged as you do all this?
 

grober

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Many modern mercs have fusible links [ prefuses] before the actual fuse blocks- and these are often poorly documented. I wonder if one of those has gone faulty. One that's often cited as causing problems is under a protective kick plate in the passenger footwell. see under the prefuse section here
Fuses - W220 S-Class Encyclopedia
 
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steveskeggy

steveskeggy

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Many modern mercs have fusible links [ prefuses] before the actual fuse blocks- and these are often poorly documented. I wonder if one of those has gone faulty. One that's often cited as causing problems is under a protective kick plate in the passenger footwell. see under the prefuse section here
Fuses - W220 S-Class Encyclopedia
Yes, thats what I am thinking.
I have found the feed from the battery, it is down the drivers side (Right hand drive) not the passenger side, as WIS and the rest of the internet says.
I have also spotted a heavy duty wire running from that side up to the dashboard, I cant see any more until I remove the throttle pedal, and unfortunately its raining, so it goes on hold until we get a dry day (Typical British Bank holiday weather!).
Thanks
Steve.
 
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steveskeggy

steveskeggy

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OK, bit of progress, and a lot of cursing.
After spotting that heavy red battery cable, i decided to look behind the drivers side carpet to see if the prefuse was there.
Removed the throttle pedal, trim, and then struggled like hell with the carpet, it has a re-inforced foam block on the back, which I had to peel off, which was not easy, and because I didnt want to strip out the whole interior, I had to make two cuts to the carpet, I dont think these will be too noticeable when the carpet is back in place and the mats are in.
Eventually, there it was (see picture)!
I removed the 10mm nut, but the thing would not move, so gave up for now, that will come another day.
Its not too clear on the photo, all the wire/cables are red,
There is one with a black plug.
One with a white plug.
One which looks like a red plug that I believe isnt a plug but a clamp connector, like what is under the drivers side SAM (I would imagine this is the feed to the SAM).
Three connected to a single post.
And the main feed from the battery on its own post.
All of the cables were live, except for the one with the black plug, which was dead.
So I then released the EIS, but didnt remove it.
There are 4 thickish wires together, the same gage as the ones coming from the prefuse, one green/black, two red, and one white/red.
All were dead, until I turned on the ignition with the keyless go button.
Then the green/black, and the white/red both read 12 volts, but the two reds were still dead.

By then my legs had given up, and it started raining, so I called it a day.
I think having a dead wire on the prefuse, and 2 dead wires on the EIS is too much of a coincidence.
I have ordered a replacement used prefuse from SMG parts, there are a couple of other things I can try in the meantime to see if this is the cause of the problem.

Thanks
Steve
 

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steveskeggy

steveskeggy

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That F%$£$%G thing has been the biggest pain in the A%%$%E this morning!
It has a ten mm retaining nut, same as the one in the rear, now like ther rear, you would think that all you needed to do was remove the nut, and the whole lot should come away from the bulkhead.
Oh No! Not this one doesnt!
I have tried all I can thing of, besides getting a blowtorch and burning it out.
I ended up managing to take off the cover, which was a job in itself for me.
I tested the fuse for that dead wire, and yes it had blown, then I tested the continuity between the dead wire on the prefuse end, and the two dead wires on the EIS.
There was continuity between the wire, and the two on the EIS, so it confirms my theory that there was no power going to the ignition side of the EIS.
I tried everything to remove the rest of the prefuse, I managed to get the guts out, leaving only the plastic base plate, but I cannot move that, even with a crowbar.
If push comes to shove, I will use my air chisel, and get it out.
One thing is for certain, when the replacement comes tomorrow, it wont be going in the same way.
I will probably use velcro!
 
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steveskeggy

steveskeggy

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Solved!
I placed the guts out of the replacement because I could not get the base out.
Built it all back up again, tried out the key, and success!
I would give one bit of advice.
If any of the fuses blow in the front prefuse, Dont try and take out the whole unit.
Take the cover off, it is held in place by the 15mm nut that holds the battery feed, a 13mm nut that holds the three large wires, and four tabs on the case.
There are two 8mm nuts holding the fuses in, if you get rid of the plastic part of the fuse, another fuse will fit on nicely without having to remove the metal parts.
The other larger fuse is held in place by a 13mm nut
I dont know if this has sorted out the other problems, that is for another day.

Thanks for your help

Steve
 

grober

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Result! glad you got it sorted. :thumb: the prefuse unit might be glued to the floorpan?? These prefuse units are poorly documented by MB :(
 
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steveskeggy

steveskeggy

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I have no idea, and I dont intend to find out!
Its easier to either swap the guts, or swap the fuse.
Unfortunately, it has not fixed the problem with the transmission lock, or the brake lights, which seem to be stuck on constantly, so I guess the next step is to pull the brake light switch.
As I said, it has been stood for two years, but I put two dehumidifiers inside to try and stop condensation, I guess they didnt stop it all, and thats why I am having these troubles.
 

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