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Electrical woes - wondering if there is a common reason

2K views 35 replies 5 participants last post by  mrboca 
#1 ·
Good evening all,

I recently acquired a 1996 E300D and received wonderful support on here last week about vacuum related leaks causing a CEL.

I'm know wondering if there is something about the electrical system in this car that is causing multiple issues at once. Currently, my sunroof, my right/left mirror adjuster, my door lock switch and my rear headrest switch are not working. When I click any of those switches nothing happens. Also, neither the front or rear dome lights come one when the doors are open even when the dome switch is set to have them come on with open doors. The windows all work as they are supposed to.

The only other thing that may be related is regarding starting the car. The first time I start it in the morning it is very quick to start but sometimes later in the day it will turn over a few times in order to start. It still starts but does sound a little labored. The battery was changed 10,000 miles ago so I don't think it is the issue but haven't tested it yet. I don't even know if that is related but did read on some posts that a poor battery can cause some electrical issues.

I've checked all three sets of fuses and didn't find any that are blown. I'm just surprised to have so many non-functioning electrical items all at once. I understand that it may be individual problems but based on my experience with vacuum thought it might all be related.

Thanks so much, Skyler
 
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#2 ·
Longer cranking on those diesels when hot is common.
We discuss it before and could not figure out reason.
I suspect software program, but no way to confirm it.
Now you locks and headrest operate on vacuum from PSE pump, so this is worth checking.
For light check the door switches.
I guess you can leave sunroof for later.
 
#3 ·
Hello again,

The electrical problems you are having are all internal to the car and they are all controlled by the Body Control Module (or Combination Control Module or CCM). There are problems you reported such as central locking switch, and dome lights, rear head rest which involve also the PSE functions and the CCM communicates with the PSE over the CAN buss (something like a local area network).

In general to isolate the problems the approach would be:

1) check all the fuses that power the modules involved. You said you checked 3 sets of fuses, however there are 4 sets (under hood drivers side, under hood passengers side, driver's side dashboard end, under rear seat). Also checking the fuse continuity may not be enough, you also need to check if there is power on those fuses at the load side (some are hot all times, some are with the key in, like the mirror control)

2) check alternative activations. For example the central locking switch does not work. Does the remote control and key lock / unlock work? The dome lights do not come on with doors open. Do the dome lights turn on with switches ? Do the courtesy lights come on when the door is opened? The mirror switch does not work. Does the mirror control work with the memory settings (when you press any of the memory settings do the mirrors move ?

3) check the grounding for the switches. Typically, the switches signal battery / ground or some voltage level to the CCM. If you have no ground / battery connection to the switch assembly, there will be no signal, and no operation. If the device (such as the mirror) operates by alternative means then you isolate the problem to the switch.

4) check the operation of the switches. Sometimes the contacts corrode. I had problems with my Lexus mirrors, and it turned out to be the mirror control switch. A spray of electronic contact cleaner solved the problem.

5) The problem may be with the CCM or PSE. The modules may have partial failures like stuck relays, internal fuses, etc. You can verify the operations of functions by alternative means as mentioned.

The engine starting issue is not likely related to the above Body Control functions. I do not have a diesel so I have not experienced it. However, if I have a problem like that, I would check the readings from sensors like the Incoming Air Temperature sensor, coolant sensor etc.
 
#4 ·
Thanks to both of you for the responses.

That gives me plenty of information to get started. In response to what Kajtek1 mentioned, when I first bought the car I had to open up the vacuum pump for the locks and found a hose disconnected. Perhaps some of the electrical connectors to that pump are messed up since the door locks all work but the two switches don't.

The dome lights do work when I switch them on but don't come on when any of the doors open.

I'll try some of the methods of checking you mentioned, MrBoca, and will see what I discover. I was surprised to find so many items not working all at once. I am fairly confident that my sunroof worked when I bought the car but I spent quite a few weeks doing other repairs so am now having trouble remembering for sure if it was.

Skyler
 
#5 ·
If your door courtesy lights do not work, it is likely you have a blown fuse Fuse 5 (25 amps rear) or connector issues to the PSE which monitors the door switches, and communication with the CCM. The rear head rest and central lock switch not working could be due to this connector issue. The CCM receives the tri-level ( ground / level 1 V / level 2 Volt) signal from the headrest+door lock combo and sends it to PSE. If no comm between the CCM and PSE, no operation.

Your sun roof may need a battery disconnect / reconnect, and re-sych of all windows, sunroof etc. Maybe the sun-roof operation is locked by the CCM due to overload.
 
#6 ·
None of the courtesy lights are working. I checked the fuse you mentioned and switched it just in case but no change. I then tried to disconnect the battery but did not have an affect. I'll continue to look for something disconnected. I did have to fix the vacuum connector inside the PSE pump so perhaps some of the electrical connections are no longer working.

Skyler
 
#7 ·
When you lock / unlock the car with the remote, do your marker lights blink ? This confirms that the PSE talks with the illumination control module.


Then to check the door switch connectivity: Withe the car running and driver door closed, turn your headlight on, then off turn the ignition off remove the key, open the door get out of the car, close the door. If your headlights and fog lights are turned on for 30 seconds then off, that shows the door switch open/close are recognized by the PSE. If not, you have a problem with the door switch connection to the PSE (or the door switch itself). You could check the door switch operation at the connector to the PSE (grounded / open with door open/close)
 
#8 ·
possible new discovery




mrboca,

Today I replaced the batteries in the key fob as it was not working but nothing happens when I push the button with the new batteries in. The old batteries were nearly dead but new batteries obviously didn't fix it.

When I turn the car off in the situation you described, the headlights and fog lights do go on for 30 seconds (perhaps a little less).

I did make a new discovery tonight that may or may not be connected to this. In the pictures attached, you can see some residue on one of the electrical connectors to the PSE. I could perhaps signal some water damage or something else. I left the connector disconnected and the door locks still work so obviously that connector has nothing to do with them. It is bottom connector on the left side of PSE if looking at it in the car.

Does it look like a short perhaps or do you think I can just clean things up and should work again?

Thanks, Skyler
 

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#10 ·
The picture may not be the best but I don't think any of the pins are missing. When I saw the white residue on the side of the connecting piece I thought there had been a short or something. I was hoping to open up the connector to see if any wires are burned but perhaps that isn't necessary. It sounds like you think it is not something I could clean up with some electrical cleaner and try to reconnect. As I said, I think all of the pins are still there but something obviously did occur in that area to leave the green and grey residue on the white part and that white residue on the black connector. I wish I knew more about electrics. I'm definitely more aware of my ignorance in that area suddenly.

Skyler
 
#11 ·
Looking at the connector again I see what you mean. They are difficult to see at the dark background. You can try to clean it with electronics cleaner or MAF cleaner (both the male and female sides) let it dry and retry. It appears that the driver side door switch working (from the delayed light test) however the PSE is not communicating with the CCM for the dome lights and the central lock. Try cleaning it as I said. Maybe it will work. Else you can open up the case and access the printed circuit board and look for water damage.
 
#12 ·
new findings

I took the PSE apart today to see what it looked like internally. I see now that one of the pins in that area with residue is slightly shorter than it should be. The tip must have either broken or perhaps was burned slightly.

On the circuit board itself I took some pictures of what might be damage to some solder points. There is blue discoloration. I'm not sure if that is normal or not. They are the points where on the other side the wires connect that connect to the top of the vacuum pump itself. Since the vacuum pump seems to be holding vacuum and is able to provide vacuum to lock and unlock the doors maybe this is not an issue.

Considering the shortened pin, perhaps this pump is not fixable but my concern also is that if I get a new pump off ebay, will it have to be reprogrammed. I was hoping to fix this if I will have issues using a new pump and my key fob won't work with it.

Skyler
 

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#13 ·
PSE provides several functions related to vacuum assisted functions, as well as electrical (locks, Alarm, trunk operation etc.) Your PSE partially works and maybe you can repair it if you can replace the pin. The PSE for your car is plug and play. there is some coding but this is mostly irrelevant (such as timing of the delayed headlights etc.). The remote operation is not handled by the PSE but handled by the RCL module (where dome light is) the RCL communicates with the PSE to lock / unlock.

Have you tried operation with the cleaned up connectors ? Maybe there is some disconnect at the solder joint at the PCB. You could trace the connection and repair.
 
#15 ·
I tried to resolder those connections and clean up anything else that didn't look right. No change whatsoever. I did try disconnecting/reconnecting the battery to see if that made any difference but sadly not. Before buying a new pump I do want to look under the hood under that box on the passenger side. I assume that the computer that the PSE communicates with is under there. I just want to make sure there are no burned looking connectors on that side that might have caused or resulted from the problem at the PSE side. It is a little frustrating not to know if the damage I found to the PSE is actually the problem but hopefully a new PSE will solve it. I find it strange still that the pump can lock and unlock the doors and also works for that turning on of the fog lights for thirty seconds. It means some communication with it is taking place but I guess not enough.

Skyler
 
#17 ·
The only link between the PSE and the CCM (as far as I know) is through the CAN bus interface which is pretty low voltage (less than 5 volts) and is well protected. You can test if the CCM-side CAN bus interface works by operating your seat adjustments at the driver and passenger doors. These modules talk to CCM via the same CAN bus too. If these work, it isolates the problem to the PSE. This however does not mean all the functions on the CCM are OK. You reported non-working mirror switch too, which is handled by the CCM..

Life would be easier if you had access to SDS equipment to check your modules and CAN bus issues through the diagnostic port.
 
#16 ·
I would be highly suspicious of the headlight switch as it can cause all kinds of seemingly unrelated electrical gremlins courtesy of your Command system.
I dx mine with Mercedes Star C4 software. Found one on eBay for $20, not super simple to replace, plan for an hour and patience.

On mine brights, all interior courtesy lights, fogs, switches would not light up.
 
#18 ·
Had a rather disheartening afternoon with the electrical story. I bought a used PSE of ebay that exactly matched mine. When I put it in and disconnected the battery for 20 mins just in case needed a reset, I found no change whatsoever. I was so hoping that after finding what looked like damage to my PSE that a new one would solve at least some of the issues but no luck. The new PSE has none of the signs of water damage or any other malfunctions that the other had. All of the functions that worked with the old one work with the new but none of the ones that I'm missing. It still seems so strange that so many stopped working at the same time: courtesy lights, door lock switch, headrest switch, sunroof, mirror switch.

Perhaps my only option is to either send to a shop or somehow get a hold of a scanner to try to read for possible issues.

Skyler
 
#20 ·
The seat adjustment and seat memory functions seem to be working.

I'll try to clean the CCM connectors. That wasn't something I had checked yet so sadly am not sure yet which unit the CCM is. I'm assuming under the hood in that box on the passenger side.

Skyler
 
#23 ·
I took out the CCM and opened it up to see if there is any evidence of a problem on the circuit board or anything similar. I cleaned off all of the connections and then put it back in. Everything is exactly the same.

I think that Drbobme1 is correct that I would have to try to determine what things are on a common circuit.

It seems as though the CCM works for certain communication with the car:
Windows work flawlessly
Lights come on for 30 seconds after I turn off car at night and exit car
Power seats work and memory functions seem to also
Locks do work with key

What things don't work are probably on a shared circuit since seems too strange otherwise that not functioning all at the same time:
Sunroof
Door lock switch
Headrests
Mirror adjustment
Courtesy lights and dome lights when open door
Key fob won't unlock/lock doors

I'll have to search around the web to see if I can find some schematics. I wonder if I should check at the other end of that connector to the PSE, the wires in the area where I found the residue and partially broken pin. Perhaps there is a short at the other end of that unless those wires go all the way to the CCM.

Skyler
 
#24 ·
The common module is the CCM, and it is a bunch of input / output circuits, drivers, relays and maybe a common control. Things like sunroof and mirror control are discrete functions the central door lock, headrest drop, courtesy lights remote lock / unlock, dome light operation (when doors are open) all go through CCM and signaled to/from PSE via the Canbus. So if the canbus interface for the CCM is bad, none of these functions work (except the manual dome light operation which is local to CCM and you confirmed as working)

The sunroof issue may start working with battery disconnect / reconnect and re-synchronization process (just like the power windows re-synch after power disconnect. Maybe you can try it.

The mirror adjustment is probably a switch / fuse / grounding issue ( check the ground point at right front seat cross-member location)

Does your defogger work ? How about trunk release at the center console ? Both are through CCM to PSE controlled functions
 
#25 ·
Could someone confirm this: Am I correct in thinking that what was visible on my PSE connector looked like water damage? There was green residue on the connector and also some grey residue below the pins on the white surface. I attached pictures in a previous post. I've been reading up on the fact that if any of the modules on the bus line malfunction then there can be weird electrical issues in any other part of that is connected to the line. It seems strange thought that changing the PSE and cleaning up the connectors didn't seem to make any change. Perhaps the problem is with another module but is strange that the PSE definitely looked it had had some electrical malfunction in that area.

I also wanted to confirm that there is no special method of resetting the CCM. I disconnected the battery for 20 mins with no effect but perhaps it is more involved to reset these systems.

Thanks for all the support
Skyler
 
#28 ·
The CCM is involved with the sunroof and the mirror adjustment. Someone had posted a list from Mercedes of all of is functions so that is why I'm thinking that perhaps many of these issue are inter-related.

The trunk open switch is another casualty of whatever is going on electrically. I wish I understood better how that water damage or whatever it was on the PSE may have shorted or damaged something else. I will start checking other modules for possible malfunctions elsewhere but that was certainly a possible cause of electrical problems along the bus line.

Skyler
 
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