[Skylaw]

Member television has posted an excellent troubleshooting guide for the CAN Bus at http://www.benzworld.org/forums/r230-sl-class/1988297-230-can-bus-how-test.html

While posted in the R230 forum, its steps are applicable to the W220 as well. Television will add voltages specific to the W220 in an upcoming addition to the thread.

The thread has been added to the Encyclopedia.

Thanks, Malcom!! :thumbsup::thumbsup::bowdown:

 

[Orre]

Hi.

As I haven't found any W220 update I'll post my own findings here. Maybe it'll help someone…
I do write this according to what I have learned about my own 2001 W220 S400CDI, so please correct anything that might be wrong. Also, I do not know if there are differences with other W220 models?...

My goal was to find out where a battery drain problem came from, as I couldn't find it via the fuse boxes. This is when I learned about troubleshooting the CAN bus system for not going to sleep when parking the car.
It is quite easy to do, and does not require more than a voltmeter to test!

But first of all! Troubleshooting battery drain by pulling fuses, is NOT the best way in a modern car with all this electronical equipment and wake-up hassle, and I wish I had learned this a bit earlier!...

1. First you have to get your car to sleep. You probably will need access to the trunk, under the hood, both front doors, and rear right door. So you need to open them all up, then close all door/hood/trunk latches with a screwdriver or something. Then use some strong tape or a needle to keep the door-lights of. (I don't know if that is mandatory?). Turn off the alarm. Then finally lock the car with your wireless key and put it away.
2. Now you'll have to wait about 30-60 min. for the car to get to sleep.
3. As an ordinary multimeter usually is fused by 10A. (Ampere) it IS easier to use a clamp meter, but if you do not have this, just disconnect your ground wire from the battery, set your multimeter to the 10A slot setting, and connect between battery negative pole ( – ) and the ground cable. If the car uses more then 0,06A. (60mA.) when asleep, you should look for a drain!
4. Take your other multimeter with really nice and sharp thin probes and set it to millivolt (mV). Now go and measure all your fuses by putting one probe to each side of the fuse. If the circuit does NOT use any power, the multimeter will go to 0 in a second or five. If the multimeter shows any voltage what so ever, there is a power draw on that circuit!
5. Note what fuses shows activity, and when done you can go back and pull those fuses, wait for car sleep, and go look at your battery amp-meter if you have found the problem(s).

You can find tables of how much e.g. 0,2V. on a 10A. fuse implies as draw on your battery. Search for something like "Fuse voltage drop chart".

Here is also a YouTube video explaining the procedure:

If you, like me, did NOT find the draw, you might want to keep troubleshooting the CAN bus system.

First a few words to get an understanding of what CAN bus is…

CAN bus (Controller Area Network) was developed by Bosch in the 80's as a way to save on copper, and has been used in Mercedes production vehicles since 1991. Today the use is comprehensive in most all electronic equipment in a wide spectre, and is mandatory in the car industry!
It saves on connectors, pins, sensors, weight and of course cost, and is additionally fast and quite immune to interference.

The CAN bus system is basically a digital network connecting devices and microcontrollers, multiplexing data without the need of a host computer.
By this ALL Electronic Control Units (ECU/ECM) in the car is connected, and might as a result give us some headache when trying to localize a problem…

CAN bus networks is transmitting data according to priority, and CAN C (engine/chassis) has 1'st priority and highest speed. (125kbps/500kbps) This is used for all safety components and the actual engine running.

The Electronic Ignition Switch (EIS/EZS) works as a gateway between networks, and will if necessary, (like if there is a shortcut) use "the other network" to get the job done.

When it comes to finding problems with battery drain, this is often connected to the "Wake Up" system of the car, where components are not actually going to sleep because some device is malfunctioning and keep sending wake-up calls in the network. This again could produce all kinds of problems that may or may not even be related!...

CAN B (interior/body) transmit with 83kbps, and is the one where these problems usually are, and therefore the only one we are talking about here.

This is quite easy to get to, and does not require more then a voltmeter to test.
On the W220 you would be looking for one green and one white cable going together. (CAN High and CAN Low)

With an oscilloscope their signals would look something like this:

So now to troubleshooting it.

With a multimeter showing Voltage, even if it is slow, you should be able to see if you have constant voltage or if it is jumping between those APROXIMATE numbers. (I found rather 12V./0,2V at my car)

In the W220 CAN High is the green cable. CAN Low is the white one.

First, be aware thee is NO CAN bus cables at my OBD2 pin 6 and 14 as I have seen described for other models!
Also, there is no CAN troubleshooting in the Xentry DAS as I have found… That might be different with newer cars then mine 2001 model?

I haven’t checked, but you should be able to use an ohm-meter to check that you have a complete CAN bus. It should have one 120 ohm resistor parallel in each end, so the ohm meter should then show 60 ohms.

The CAN bus B network system is connected like this:

Here is an explanation of device codes:

Units connected to X30/6

N73 – Electronic Ignition Switch (EIS / EZS)
N80 – Steering Column Module (SCM)
N22 – Automatic Air Conditioning (AC / AAC)
A1 – Instrument Cluster (IC)
N72/1 – Upper Control Panel (UCP)
N10/7 – Right front Signal Acquisition Module (SAM)
N10/6 – Left front Signal Acquisition Module (SAM)


Units connected to X30/5

A37 – Pneumatic System Equipment (PSE)
A40/3 – COMAND
N22/4 – Rear Automatic Air Conditioning (AC / AAC)
N32/1 – Left front Electric Seat Adjustment (ESA)
N69/1 – Front left Door Control Module (DCM)
N69/3 – Rear left Door Control Module (DCM)
N10/6 – Left front Signal Acquisition Module (SAM)


Units connected to X30/4

N10/8 – Rear Signal Acquisition Module (SAM)
N70 – Overhead Control Panel (OCP) -via N10/8
N69/2 – Front right Door Control Module (DCM)
N69/4 – Rear right Door Control Module (DCM)
N62 – Parktronics
N32/2 – Right front Electric Seat Adjustment (ESA)
N25/6 – Rear seats Electric Seat Adjustment (ESA)
N88 – Tire Pressure Monitor (TPM)
N69/5 – Keyless Go control module (KG)


Those X-connectors are some black plastic connections that you will find as follows.
All of them with plugs with green and white cables in now particular order. You have to "clip open" the connector to be able to unplug device plugs. It can be a bit tricky, but does not require force. (you might gently pry with a flat screwdriver) The "lid" goes sideways and has one "clip-lock" at each end. Underneath it reveals two metal-strips that corresponds with all green and white wires, so it is easy to see with just one measure if there are any devices keeping up activity in that particular connector.

First one X30/6 you'll find above the left side of the brake pedal. There is no need to take of anything but stick your hand in the back of the rubber cover above the pedals. If this is ok you move forward to X30/5 -then to X30/4.

Next X30/5 under front left sill.

X30/4 under front right sill

I do not know if I have done a correct troubleshooting yet, (waiting for parts) so I probably shouldn't talk with to big of words… But as I already had unveiled some devices, I jumped from measuring X30/6 directly to check some devices connected to the other X-connectors, as it was easier to access then opening up the sills…

For me it looks like the rear SAM was the culprit. I have also read it is not uncommon to find e.g. COMAND, seats, OCP, door modules, to be the problem…

Anyway. I hope this could be of use to someone!

I'll add a couple of nice .pdf's I have found about CAN systems, which also contains some other models, and from which I have picked some pictures:
MB CAN
Mercedes CAN diagnostics

Also, here is a nice site with most devices listed together with pics:
Components

And finally, I would also like to add a sentence I have picked up about battery-drain, where the EIS itself was the culprit. (this is where my DTC's pointed, so I still hope this is not the case…) Maybe it could be of use.

The other problem of 2155450808 and 2155450908 is electric leakage symptom. Maybe you will find it is difficult to start the car after parking your car whole day. It is caused by CPU instability, the gateway running all the time can’t switch to asleep mode, and EIS gateway cannot be off when EIS have been turned off. All CPU are running, so it will lead to electric leakage symptom. Many workshops don’t understand the reason, the just add switch near the battery, and it is inconvenient for owner to operate. The solution recommended is to replace 1L85D and 3L40K chip.

All the best!
/Orre

 

[Dave2302]

Hi,

Excellent Work, and that MB Doc you found, I have that printed in a file somewhere from waaaay back, I believe it is linked in our Encyclopaedia

You now have a far better understanding of your Car :smile

 

[Orre]

Thanks @Dave2302.

Yes I believe you are right about that document.
But it took me a while to understand that CAN bus system looks way different in different car-models, so the excellent @television guide that @Skylaw refers to does not fit the W220 at all...
This is why I found it appropriate to write a guide pinpointing this model.

I hope I didn't mess up the language too bad, and that this can help both me and others understanding cars in general better!

By the way. As I found why the heck SDS does NOT do any CAN troubleshooting, I believe this is how the OBDII may look at later years?
(In the 2001 nr.6 and nr.14 does not exist...)

 

[Dave2302]

Hey @Orre ,

I'm not knocking it, great article, and good work :smile

 

[Tiger_one]

Welp, I'm here now, been trying to find drain for over a week now. Started after a drive home in rain and I turned on seat heater (low position) for a short while. Rain sensor worked fine, no problems, all seemed fine. 2 days later after parked in garage, battery dead. Battery 2 years old, Advance Auto checked all good.

Pulling fuses is very confusing results. I have dc amp meter in series with battery positioned where I can watch while pulling fuses. Now have a dc amp meter clamp, rear SAM is using 600ma, front right front SAM using 800ma, this after CAN should be asleep. At some point my key fob quit working from a distance for opening and locking doors or trunk. Battery was disconnected several times for checking, and then series amp meter hookups.

My lowest drain WAS 600ma to 800ma, but now is 1.6amps. Have no idea what I did to make it go up. Have been all over the SDS, cannot delete codes in right front SAM (maybe a clue). Cleared all codes, resync everything and going for a test ride. See if more codes will be set.

Pulled OCP and all looks good. Pulled rear window IR antenna, cleaned contacts replaced. Keyfob still doesn't work doors or trunk unless 3 inches from driver door handle. Pulled right front SAM and removed cover, all appears well, everything I have removed looks new, no corrosion. I'm SO STUMPED!

P.S. I also removed PSE pump and tested on vacuum and checked vanes, some wear but works fine. I can hear it work and does not stay on longer than about a second or so for door closing or trunk latching. I did have some pressure in lumbar driver seat, I relieved the bladder to rule out this fault.

 

[Kraut56]

I don't know your trunk configuration, but on my car going with SDS into the trunk menu, and then selecting restore/initialize fixed it.
Happy new year!

 

[wallyp]

Only one problem, but perhaps a weak battery in the keyfob?

 

[Dave2302]

Don't forget that the Key has 3 separate ways of functioning ........................

The IR for starting when in EIS which requires no batteries.

The RF Function for C/L which does require batteries, this clearly is not working.

The IR Function which operates Global Open / Close, again requires batteries, clearly this is working and yes depending upon ambient light it has to be close to the IR receiver in the Door Handle


My best guess with the current info is that something has got water ingress and the Antenna Amplifier is not working properly.

Disconnect the main power feed at rear SAM first and see if the drain drops, if so move on from there.

Don't forget whilst diagnosing, anything that is open, like the Trunk, Bonnet and Door Latches need to be latched Shut with a small Screwdriver

HTH,

 

[Tiger_one]

All good ideas, and will try them all. I have trunk, right side rear door and hood up, locked and light blocked. Getting some interesting results with the voltage drop across fuses as per the post above.
Did replace batteries in key fob, but wife's key fob quit working also.

Being i'm now at 1.6amps drain, reckon the CAN is not sleeping, so some unit is keeping it awake.

My fuse chart that was in the trunk doesn't agree with some of my fuse locations and sizes, so that doesn't help.
I will post when I find the culprit.

 

[wallyp]

If you go to the "Encyclopedia" that is shown in the blue "sticky" threads at the top of the first Forum page, then drill down to the electrical/electronics threads, you will find a selection of fuse/relay charts, and perhaps find one that matches your car.

 

[Tiger_one]

If you go to the "Encyclopedia" that is shown in the blue "sticky" threads at the top of the first Forum page, then drill down to the electrical/electronics threads, you will find a selection of fuse/relay charts, and perhaps find one that matches your car.

Yes, have seen that, also have one up on my TV screen from youtube. Some of the fuses I don't have, and others are wrong sizes for # fuse.

With rear SAM disconnected, I am still draining 800+ ma. Rear SAM disables both front seats controls. I do have a 5amp fuse showing 4.5mv drop at #6 which fuse chart states instrument cluster??

 

[Tiger_one]

Checked faults in AAC (charcoal button and REST button), B1000.

B1000 Control unit N22 (AAC pushbutton module) is
defective.

The fault on SAM front right is B1416 which is A31/m1 which is the coolant circulation motor for N22. This lies I believe right behind my chinese HU I installed couple years ago. Late and cold in the garage, I will investigate in the morning. Hope this is not a deadend.

 

[wallyp]

The only coolant circulation pump that I have seen is outside in the engine compartment, between the two firewalls at the center rear of the engine bay, under the wiper motor.

 

[Dave2302]

Use Starfinder on SDS to find the exact location of A31/m1 ....................

However IIRC @wallyp is bang on the money, it certainly isn't behind the Head Unit

Also unless for some weird un accountable reason it is running at all times, I doubt that will be the cause of the parasite, but it's very unlikely it is permanently running, they usually just don't run at all

HTH

 

[Tiger_one]

Head unit is OK. Nothing behind it like @Dave2302 said. N22 had dirty noisy fan, cleaned and checked thermistor value 53k ohm. All OK. After drive for 45 minutes yesterday, no faults.
No change in parasitic draw of 1.6amps. When this all started a week ago or so, I was only drawing 200 or 300ma and the key fob was working at distance for everything. So loosing the key fob must be a clue.

Where is the antenna booster???

 

[Dave2302]

Antenna Amplifier gone bad ?

200 or 300 mA is way too much, let alone your current (pun intended) figures

BTW total current draw when vehicle is asleep should be circa 40 - 60 mA depending on exact vehicle spec, the more goodies the more the draw ................

That is to say 0.040 to 0.060 Amps

HTH

 

[Tiger_one]

That is what I meant, when the battery first went flat, I was at 300ma which was close to the less than 60ma.
Hold on, wifey just found a post where fuse #60 controls antenna booster. I have no fuse or wire to that location BUT I do have a wire to #61 and no fuse. I put a 7.5amp fuse in #61 presto, key fob works from inside the house, WOOPPEEE!!! Maybe I misplaced a fuse when checking them a dozen times, don't know.

Now to wait for it to go to sleep and check the parasitic draw. Standby.

 

[Tiger_one]

Use Starfinder on SDS to find the exact location of A31/m1 ....................

Starfinder has pictures of everything BUT the A31/m1 motor. The wiring schematic shows wire RT/WS??? White streak on (what is RT color)?

Okay, found the picture. I was able to get my hand in there to pull both connectors, still have draw of 1.6amps. Damn.

I'm now thinking I have a bad ground to SAM. I'm looking for a sensor to check reference of 5v.

 

[Dave2302]

RT/WS = Red / White

You wouldn't, (well perhaps you would), believe how much money I earn when others have been checking Fuses and Relays and they ended up misplacing them .........................

ALWAYS Photograph the Fuse and Relay Boxes before even pulling a single Fuse

You are confusing the hell outta me saying 300mA is close to 60mA ..................... never mind

Regarding A31/m1 exactly as @wallyp said, this is where it is on my RHD UK car ....

pics are clickeable:-

First pic shows the Torch, it is below that area ....



Here ....



Yours is likely symetrically opposite on a LHD Car, although I simply don't know that for sure

You will need to remove the Wiper arms and Screen Base Scuttle Trim to get at it

At this stage of the game I suggest just putting a screwdriver on it and to your ear with ignition OFF and just make certain it isn't running ...............

Like I said, yep they do fail sometimes, but normally they just don't work

HTH