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Discussion Starter #1
I have a C180 with some battery drain faults. I had a drain of .9 amp in sleep mode which I traced to the fan for the temperature sensor fan in the roof lining. I cured this by replacing the front SAM. I now have another fault which is a .6 amp drain. If I remove ALL the central locking fuses this drops to .2 amp which is acceptable i my books, but if I remove the fuses 1 at a time the drain does not drop. I am suspecting the rear sam is faulty but I have 2 questions. 1 if I replace the rear sam does it need to be cded to the vehicle? is there any known way to teat bthe rear sam?

Also should the front sam be coded to the vehicle?
 

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.2 amps will still drain a battery probably overnight. Acceptable would be less than 0.05 amps. I've never seen any central locking issues cause a battery draw, but you never know. Most commonly would be either front seat control modules (if equiped with power seats), A bad Comand unit if equiped, PSE phone module if equiped. If you access one of the CAN blocks (say the one attached to the top part of the driver's side underdash panel) and check the voltage at one of the pins (positive to either the high or low CAN pin, and negative to a suitable ground), you can test to see if the CAN system is going to standby mode, or staying awake. If it's around 1 volt or 11 volts (depending on whether your testing high or low), the CAN system is active, but with all door closed and key out of the ignition, it should change to about 4-6 volts on either pin within 1 minute, signalling that its now asleep. If you have absolutely no idea what I'm talking about, you might want to take it somewhere.
 

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After I owned my 2000 CLK320 for about a year I had to leave it parked for extended periods, sometimes up to three months or more at a time. It always fired up very healthily on first crank after all this time and neglect. (I think it was glad to see me!). You can calculate the low drain it must have had. The battery performance is still as new after 6.5 years.
 

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Discussion Starter #5
Zewerr said:
If it's around 1 volt or 11 volts (depending on whether your testing high or low), the CAN system is active, but with all door closed and key out of the ignition, it should change to about 4-6 volts on either pin within 1 minute, signalling that its now asleep.
Update:

I cant find the can block you speek of and to be honest if I could i have no pin outs on this unit. I have tried checking the high and low can volages on the front SAM as I have pinouts for this. Connector 10 pins 4 (brown) and 5 (brown with red trace) . Connector 20 pins 1 (brown with red trace) and 2 (brown). I have found that when I have a current draw of around .7 amp (with the dors locked for 5 mins) the brown wires have around 4.5 volts and the brown and red have around 0.5 volt. If however disconnect and reconnect the multiplug for connector 20 the current draw goes to 0.02 amps and the voltages go to 0.00 volts on the brow and red wires and 11.52 volts on the brown wires (battery voltage is 12.02 atm).

Question 1 (and I hate to doubt you) are you 100% certain of the can high and low voltages you quoted me?

Question 2 do my voltages look correct?

Question 3 I guess I am looking for a can module functioning incorrectly on the circuits for connetor 20 on the front SAM does this sound correct?

Question 4 do have an exact location of the can module you specified and pinouts?

Thanks for the continuing help.
 

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delambo said:
Question 1 (and I hate to doubt you) are you 100% certain of the can high and low voltages you quoted me?

Question 2 do my voltages look correct?

Question 3 I guess I am looking for a can module functioning incorrectly on the circuits for connetor 20 on the front SAM does this sound correct?

Question 4 do have an exact location of the can module you specified and pinouts?
#1: Haha, nope!!! I typed that thing all from memory, and whenever I tested a can system to see if it goes asleep, I always tested it by testing the voltage with it active, and see if it changes within a minute. The voltages I gave you were from the best of my recollection. Now that you have mentioned it, those voltages do sound about right.

#2: I guess I just answered that.

#3: I don't think testing the voltage at either of the SAM connectors would be a good way of testing the CAN system, since soooooo many functions of the vehicle are controlled by the front and rear SAM. See #4.

#4: That was one thing I was gonna ask you if it was right or left hand drive. On a LHD, which is all that I work with, the CAN block is under the driver's side underdash panel (black panel, infront of the pedals), which is removed by the 3 torx screws, and I think one plastic retainer, with the hood release and the OBD II connector attached to it. I want to assume that it would be still under the driver's side panel on a RHD vehicle, mainly since the main control module that acts as a gateway between the engine CAN and the chassis CAN is the EIS. But maybe it's on the left side on all the cars. There should also be two more CAN blocks. underneith either side front lower door sills. If you removed them, you'll see a black wire harness housing with a bunch of access panels on it. If you open up the panels and dig around, you should find a CAN block in there. CAN blocks can be identified by basically a whole load of CAN wires wired into it (CAN wires can be identified by them being twisted up in pairs). They should always have some open ports, so they're great for testing, since you don't have to unplug any modules to test it.

I'm curious, does this car have power seats?
 

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Discussion Starter #8
Yes the car does have power seats but only for the backrest position and forward backward control with no memory. The controls are on the seat not on the door.

I have found the can block you talk of and am investigating it now.

The connector 20 which when unplugged and reconected that causes it to into sleep mode has connections to the light switch terminals 1, 2, 3, 4, 10, 11, 12, 13 + 14. Also to EZS control unit pin 4 and the parking brake switch. I have tried uplugging and reconnecting the light switch to eliminate that but it doest go into sleep mode so im now going to inestigate the EZS and paring brake switch.

Thanks for the advise so far...
 

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Discussion Starter #9
UPDATE

I have now disconnected each of the wires one at a time from the connector 20 to the front SAM and have found that the car sleeps only when the CAN high and CAN low are disconnected the car sleeps. None of the other wires disconnected put the car in to sleep mode. I have found which pair of can cables go in to the can block as discussed and I have found that when disconnected it disables the remote central locking system and puts a faulty display messge on the screen. From this I assume this carries bus messages for the central locking system and the digital dash. I have found another pair of can bus wires on the same CAN block that when disconnected cause the car to sleep. When disconnected it gives a brake fluid warning.

I dont know if this helps at all.

Thanks.
 

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Discussion Starter #10
Oh also with regards your query about the power seats I have just noticed that the seats still operate even with ALL the plugs out of the CAN block in question. I dont know if this helps at all.

EDITED

Perhaps that is beacuse I have tried the drivers seat with them all disconnected and not the passenger seat!
 

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Discussion Starter #11
Right I have now returned home where I have some wiring diagrams and pinouts. According to my info it should have 11 possible connections on the CAN block (or as my info calls it the canbus potential distributor) of which up to 9 are connected depending on the options fitted to the vehicle. Here is what my info says should go to each plug.

1) does not specify just says Can high and CAN low
2) Right rear door control module (remember this one is right hand drive)
3) Right front door control module
4) Airbag control module
5) Teleaid/telephone tranceiver OR ecall control module
6) Multifunction unit
7) not connected
8) park distance control module
9) Passenger seat control module
10)Park heating unit
11)not connected

3 questions to ask 1, does it really mean passenger control module since the drivers side can block seems to control items on the drivers side of the car? 2 what does it mean my the multifunction unit? Does it mean the front SAM? 3 where does terminal 1 (CAN high and low) go?

Not all of these are connected on the vehicle I am working on I think from memory only 5 or 6 are connected but I can say for sure it doesnt have PDC or a telephone.

I have a horrible fealing though that the 2 connectors that allow the system to go in to shut down mode if disconnected and re-connected will be numbers 6 - multifunction unit (which I think is the front SAM) and 1 - CAN high/low (which I am guessing means it goes to another CAN block or canbus potential distributor) which leads me no closer to the answer if this is the case.

So can anyone tell me where the other can blocks are (if there are other can blocks) and what each of them serves? Also does anone have a decent wiring diagram that they could email to [email protected] or [email protected]? Or does anyone have any other suggestions as to where to go next?

Thanks again.
 

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Discussion Starter #12
I think I found the problem. The drives door module. When I unplugged the bus line to the door module it went into sleep mode nicely. Since I re-connected the bus line to the drivers door module it has stopped locking and unlocking! Have ordered a new one and we shall see if that fixes it on monday!

Just a little pointer to zwerr though (and thanks for all your help) I forgot my multimeter today so I had to use my oscilloscope. Using a scope makes things even clearer because when the vehicle is awake you can clearly see the CAN pattern and when it asleep it just goes to flat line.
 

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Yeah, when you hook up a multimeter to an active can system, it's constantly sending a binary code, so it's on/off/on/off all the time. When you see 4-6 volts with a multimeter, your just simply seeing the average voltage of it. That's kinda cool you got to see that. Hopefully, you've found your problem.
 

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After several cups of tea and lots of head scratching I decided to take the car fo a test run to see if the system needed to learn since I have been disconnecting CAN lines and now I have a result. The car now goes to sleep when double locked but not when single locked! Oh well at least I getting there slowly!
 

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You mean it will sleep only if you press the lock button twice? Well, the main control module for the Central Locking is the EIS, which is pretty much the brains of the whole locking, drive autorizing, as well as the CAN system. There may be a good possiblility you have a bad EIS. I'm wondering if there might be some version coding issues with either the new door control module or the EIS that may be causing your problem.
 
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