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Interior light drives me crazy.

3K views 18 replies 6 participants last post by  WillS 
#1 ·
Hello MB friends
This is a long one, sorry.

My car, an S210 E300TD, 1998, has suddenly decided that it does not want to turn on the rear dome light, and the light in luggage compartment, when the tailgate is opened. The problem occurred suddenly, without any prior notice or indication of any problems.
I live in Europe, so obviously the car has Euro-specs.

I have now spent several whole days trying to troubleshoot the problem, without success.
The first thing I did was to check all fuses, no fuses blown. The next thing checked were plugs and connections on various devices like rear door switches, shutting assistent module including the micro-switches inside the locking mechanism in the tailgate, the PSE and SAM module under the rear seat. Everything in order with no visible defects, nor are there any signs of moisture or corrotion inside the modules, or anything that suggests that there ever was. I have measured the current to and from the various modules, as directed in WIS, and nothing, apparently, do anything wrong. The next step was to replace the PSE module A37 as several forums refers to this as one of the most likely causes of error, for issues with central-locking systems and interior lights, again without any success since the new (used) module has exactly the same bug, no interior lighting when tailgate is open . I realize that it can be risky to replace with used devices, but the probability of the second PSE module should have exactly the same issue like the original one, is very unlikely, or what?

Another suspect I have in this regard, is that the fault might lie in the electronics inside the shutting assistent unit itself, but the shutting assistent works flawlessly, and I do not really want to spend a pyle of cash, just to find out that the old unit worked fine. I have had the micro-swicthes out of the lock and connected them directly on the wires in the tailgate, brown/yellow and brown, without success, and I have of course checked for resistence in wires and defective switches, nothing. I have ohmed wires from the PSE A37 to tailgate unit, to the rear interior lights, for various chassis mass points to check for broken, cracked or disconnection of cables, yet everything seems to be as it should be.

And it's the most interresting issue of all. EVERYTHING works as it should. Power-lock, remote controls, power windows, both manually and by remote, interior lights when the rest of the doors is opened, and it shuts off as it should do, with delay. I can manually turn on and off the cabin lights, both front and rear, with the controlles in the ceiling or with remote control. The only thing I have noticed is that the car apparently can't detect when the tailgate is open. It flashes 3 times when locked, tailgate open or closed, and the re-lock function works perfectly even if the tailgate is open. But open doors are recorded through the door contacts, so it's probably not that surprising.

The only thing I can think of is that the fault may lie in the rear SAM, but again, what is the probability for that this module wouldt have ONLY one defect, wouldn't there be other issues that could indicate that this device was defective?
Another thing is the upper light controle module N70, behind the mirror. But if I read my wiring diagram correctly, this unit only have 2 Can-connections, can-H, can-L, to the PSE module A37, via a Can-Bus connection, X30 / 7, through the N72 "Steuergerät Unteres-Bedien-Feld", but I suspect that these units are working corretly, because I can measure 12 volts on the light units in the trunk when they are off, and less than 1 volt when power is on, tailgate open or closed. And again, if there was fault in the Can-Bus system,wouldn't there be other indications of this?

There are not retrofitted equipment of any kind in the car, either original or non-original (except for an Alpine radio), and the car is not even equipped with things like electric seats, sunroof or ambient-lighting packages. The car is (unfortunately) quite "low-spec" which (thankfully) helps to eliminate many possible faults, (and less things to breake down) The only unit that has been replaced recently is the EZS/EIS, but it was done by the local Mercedes stealer (not cheap), they could just as well point a gun at me and ask for my money, same feeling.

I often read about problems with interior lighting that does not turn off, power-locks without function caused by interiorlight problems, alarms going off due to Interior lighting, or interior lighting that does not work at all, often caused by defect door contacts, and/ or a faulty PSE. But I have not yet found a single post that describes the same problem as mine, which apparently, (unfortunately), makes my car unique.

The next step is that I will burn the car to the ground, and piss in the ashes ...... joke ...... maybe:angel.
No really, I hope that there are some of you nice people inhere who have an idea of the problem, because my OCD forbids me to ignore this problem.
 
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#2 ·
The computer controls drive me crazy as well as there is no easy way to troubleshoot them.
That is why we hear all those stories about dealer replacing 3 modules before he figures out the sensor is bad.
Speaking of which, I think tailgate is having gravity switch for those lights and if that one shortens, the computer disables the rear light. Worth checking IMHO
Are those lights working with manual switch?
 
#3 ·
Computers, a thrill when they work, a pain in the a.. when they don't.
Thanks for fast reply, but I am 100% sure that my car is not fitted with any gravity swiches, at least not in the tailgate. The rear interior lights are controlled by the micro-switches in the shut-assist asembly. But you are right, a dodgy or failing ground connection can cause huge problems in these cars.

Christian
 
#4 ·
If the car can't detect when the tailgate is open, how can it know when to turn on the light? There's a switch in the latch assembly. You can test it to see if it opens when the latch does. Then replace the latch or fix the short circuit.
 
#5 ·
Well, it can't. That's the problem. I have tested the switch in the latch. Actually there are two switches and both are working fine. I also tested the wires to and from those switches, everything is in perfect working order. The interior light can be turned on and off by all the other doors, the switches in the ceiling, and by remote. Central locks works flawlessly, 3 flashes when locked and all. Tailgate shut-assistant also work perfectly. PSE has been renewed, because it is known to cause major problems with power locks and interior light, but in my case it was not the problem. I start to suspect that the fault may be in the Can-Bus system.
 
#6 · (Edited)
I have a 1998 e320 usa version. I have tested the trunk opening (also was an excuse to yearly lubing the lock) with the key. If the car is unlocked, when trunk opens the trunk light turns on but no interior lights. When locking with the key the interior lights turn on, when unlocking and pressing to open the trunk, trunk opens with light and the interior lights turn on (just like the door lock).

When you say the rear dome light does not turn on, do you mean the front dome lights turn on but not the rear ?

Have you checked the grounding of the A12 (tailgate closing assist) output to the A37 (PSE) Brown/yellow wire when the trunk is opened? In the A12, there is a transistor which applies ground to the PSE through this connection. Also check the sleeve of this conductor which is tied to the ground, and the transistor, when turned on applies the ground to the pulled up PSE input.


Also check that the trunk light switch is grounded at one end (at the left taillamp assembly). When the switch closes, it applies ground to the trunk light bulb and also signals the PSE. The rear dome lamp is controlled by the PSE by applying the ground.
 
#7 ·
Thank you for your interest mrboca.

My car do like this: when unlocked via the remote all interior lights turns on, front and back. When car is locked again, all lights turns off, front an back. If the car is leaft unlocked with all interior light off, and one of the front doors is opened, all interior lights turnes on. If one of the backdoors or the tailgate is opened, only the rear interior lights is activated. My car stil turns rear light on when the rear doors openes, but not if the tailgate is opened. So, to awnser your question, no the front light does not turn on, it is not suposed to do so if only rear doors or tailgate are opened.

I have cheked all the ground wires in the rear of the car, and all seems to be fully connected, and I have checked the signal in the Brown/yellow wires going to closing assist from the PSE. Acording to WIS, the function of the swicthes for closing assist and the rear interior light is controlled with a multimeter, connected between pin 4 an 13 located in the multi-connector with 20 wires. Pin 4 is constant current from the battery and pin 13 is the brown/ yellow wire going to close assistent. Actually there is 4 wires going to the coseing assistent, two brown/yellow and two brown ground wires.

According to WIS, the correct signal between pin 4 and 13 is 12v when tailgate is open, and less than 1v when closed. This i also what I have. So I am pretty sure that no wires ore swicthes are broken. Pin 10 is the D-pillar lights ground connection to PSE A37.

All signals to A37 seems to be fine and correct. Thats was exactly why I suspected the A37 unit to be faulty, and changed it whit a nother used unit, which has the exact same partnumber at the original one. But the new A37 module has the exact same problem, no interior light when tailgate is opened. I believe that if this module was defective, the problems would not be concentrated in one specific area, and confined to one single issue. An the probality for 2 of these units, having exact same defect, is very unlikely.

So I am starting to suspect either the interior light control module N70, the Can-Bus connections to the lower controle panel N72 via connection 30/7 from N70, or the rear SAM module.

Christian
 
#8 ·
I retested, and when the car is unlocked the opening of the rear door turns on the rear dome lamp (just like yours). With the trunk unlocked, I press the lock button the trunk opens and the trunk light is turns on but NOT the rear dome light (or any other).

Why do you think the rear dome light should turn on when the trunk is opened only?

The trunk light has a simple circuit. It has a switch, light, power and ground. Fuse 4 (15 amp fuse and the ground) when the light is turned on, you pull the switch down and the light turns off (to prevent battery drain when you leave the trunk open for a long time).

In the attached E18/1 is the trunk light, s17/8 is the trunk switch. so it really has nothing to do with the PSE or any other module.

This is for 1998 e300. I am not sure if it applies to the euro version.
 

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#10 ·
S210 in Europe = W210 wagon in USA.
One more tough I have - the front overhead console has manual switches for those lights.
I remember that I never could memorize how they work and ended not touching them.
Worth checking if cargo light is not turned out there?
 
#11 ·
I didn't realize S210 is a wagon, and then it would make sense for the rear dome light as the tailgate is another rear door:) If you are certain the rear dome light should turn on but it does not, maybe it is due to some version coding for the PSE. If you picked up a used PSE for a sedan, the trunk opening will not turn on the rear dome light (at least not for my sedan).

But for the tail light itself I would check the power and grounding, and the light socket bulb.
 
#12 ·
I see the attached file, and it is exactly the same diagram as mine. Only difference is that mine is in german and my german is not the best. So thank you for the file. Why do I think that the rear dome light should come on when tailgate is opened? I think that I remember that it should, but I am starting doubt that my memmory is correct. Nevertheless I still don't know why my trunk lights E25/3 and E25/4 won't turn on when I opens the tailgate. Could't the problem come from the central-locking system. Maybe I am looking in the wrong direction. Could the interior light infact be working correctly, but is affected by a fault in the central lock? Or could the issue come from the Can wires at pin 9 and 8?
 
#13 ·
I think that the PSE would have a different part number if it came from a sedan, but I'm not sure though. The unit that I purchased at a breakers yard came from a wagon. I took it out myself. But looking at my brand new wire diagram I see som unproven test options regarding ground connections. That will be something I try first thing tomorrow. Sorry for spelling mistakes and bad grammar, it is very late here, and I have been awake for allmost 24 hours.
 
#14 ·
Alright, now I see that you are talking about the pillar lights, but not the trunk light (that I was talking about). That is specific to station wagons I suppose. For E25/3 and E25/4, the PSE must apply a ground from pin 10 to turn the lights on. The lights get the 12V from circuit 30 (shown as Z7). Can you ground the wire at the PSE end (with the connector disconnected to PSE of course) to see if the lights work ? Or have you confirmed the lights working already ?
 
#16 ·
Sorry for the long responce time.
The D-pillar lights work. They turn on when doors are opend (all of them). They turn on when I manually push the buttons on the interior light controles behind the mirror. When they turn off, they fade out like the rest of the interior lights. So I know that the D-pillar lights work. Whether the rear dome light should turn on, when tailgate is opened, I simply can't remember. I think it should. When I look at the wire diagram, I see that the D-pillar lights are connected with the rear interior light via the Z7 connection (circuit 30), and the fact that they turn on when rear doors is open, makes me beleeve that the rear dome light should turn on when tailgate is opende. But again, I can't remember.

Another thing I have noticed, When doors is open and the interior lights are on, including the entrence lights, they all turn off after about 5 minutes if the doors aren't closed (Battery power saving mode), except for the entrence lights in the rear doors. I can turn them off manually whith the door contact, and they turn on again when the contact is released. Whit the doors open and the interior lights off, due to power saving mode, and the entrence lights in rear doors on, I have noticed that they turn off when the closing assistant motor is activated, only to turn on again after a few seconds. The entrence lights is powered by the DCM in each rear door, and has no obvious connection to the close assistent or the interior lights, exept from the Can-bus. Could it be that the right rear DCM is causing trouble in the Interior Can system?. Could i be that simple?
 
#18 ·
I just went out and checked mine.

I unlocked the wagon via the key fob and all of the interior lights came on. Two front domes, center dome (directly above center rear seat headrest) and the two rear D pillars.

I waited until they dimmed out completely.

I opened the tailgate and the center dome and the two D pillars ONLY came on. The front domes did not come on.


I closed the tailgate and sat in the car with the doors closed until the lights went off.

Using a flashlight, I pushed the button for the rear lights and the center dome and the D pillars came on, exactly the same as opening the tailgate.
 
#19 ·
Another Data Point

Interesting read. I checked my wagon interior lights and they behaved exactly the same as previous post. One other thing--when opening wagon rear doors, only rear center dome and two D-pillar lights come on. Also, hit the driver's overhead console manual lights switch once and all lights will not come on when any door is opened. Hit it again and normal operation is restored. Nice option when one does not want to be seen getting out of the car.
 
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