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Hello all...new Mercedes owner here and new member to the forum. I have a 1998 C230 with 105,000 miles on it...pretty good shape. I've already fixed both side mirrors (broken spring catch), driver's visor and rear view mirror so my "fix it list" is getting shorter.
The problem I'm trying to resolve now has to do with the intermittent ability to open the trunk. It appears to be tied directly to the vehicle thinking the trunk is already open therefore it will not activate the truck latch mechanism. Here's what I know:
1. The trunk release button on the center console does not work. If you lift it under any condition the trunk will not open. Sometimes the red LED is lit and sometime it is not. Yes, even when the trunk is closed the red LED is still lit sometimes.
2. It would appear that when the red LED is lit the remote control button will not open the trunk. I assume the red LED being lit means the vehicle thinks the trunk is already open and therefore will not activate the latch.
3. When the vehicle is unlocked and the red LED is lit pushing the button on the trunk will not open the trunk.
4. When the LED if off, then pushing the trunk button on the trunk will open the trunk. This is also true when you push the trunk button on the remote control.
5. If the LED is off and you open the trunk the LED will come on and stay on regardless of if you close the trunk.
6. If the LED is off and you open a door the LED will come on and stay on regardless of if you close the door. Again, while the red LED is lit you can not open the trunk by pushing the trunk button or pushing the trunk button on remote regardless of if the car is completely unlocked.
7. If you wait some period of unknown time between 10 minutes and some time longer the red LED will go out. This is true if the car is locked or unlocked. I literally have to wait 10, 20 or 30 minutes with the car sitting in the parking lot to get the trunk to open...usually using the remove control button.
Somehow, I believe my problem is two-fold: First, why doesn't the center console truck release button ever work?...clearly it has power to it as the red LED turns on and off. Second, what is causing the red LED to come on and stay on. I believe if I can fix that problem then I'll be able to open the trunk as needed using the remote button or the button on the trunk. There is still the issue of fixing the center console button.
I get the impression that this vehicle may use some sort of vacuum system to activate door locks and the trunk. Is this related to a vacuum leak? If so where would I find the vacuum system controller and the hoses? Any other ideas fellas?
Last edited by SyberTiger; 05-18-2016 at 09:26 AM.
I am not sure if there is an interaction between the switch button that activates the trunk light. Open the trunk and it should be on the trunk lid, by the latch. It may be the cause, but that is a guess. I think you can remove it, and jump the terminals to check. The vacuum unit is on the right side (Facing forward) in the trunk, underneath the wheel well upholstery. If you can't figure it out, YouTube will guide you.
I am not sure if there is an interaction between the switch button that activates the trunk light. Open the trunk and it should be on the trunk lid, by the latch. It may be the cause, but that is a guess. I think you can remove it, and jump the terminals to check. The vacuum unit is on the right side (Facing forward) in the trunk, underneath the wheel well upholstery. If you can't figure it out, YouTube will guide you.
The trunk light does not come on, which is something I had noticed before but assumed the bulb was burned out and just needed replacing. I seem to recall another thread somewhere where it was implied that the trunk light should be looked at but it wasn't clear what specifically the light would have to do with the problem.
I'm convinced that the problem is that the vehicle thinks the trunk is already open (which is when the trunk release button in center console red LED is lit). Why the designers thought it a good idea to prevent triggering the trunk latch when it's already open is beyond me. Just about any other car will let you activate the trunk or door latches when they are open.
My suggestion was just a shot in the dark, but because the electrical system is so interconnected, and the computer only does what it thinks it should be doing. If there is a current that normally relates to the trunk, maybe it thinks it is open, and just reacts.
Did you change the bulb? Did you remove the button switch and make sure it's working properly? Sometimes the simplest things are overlooked.
My suggestion was just a shot in the dark, but because the electrical system is so interconnected, and the computer only does what it thinks it should be doing. If there is a current that normally relates to the trunk, maybe it thinks it is open, and just reacts.
Did you change the bulb? Did you remove the button switch and make sure it's working properly? Sometimes the simplest things are overlooked.
For the life of me I can't figure out how to get the lens cover off the trunk light without breaking it. It looks like you are supposed to push it towards the driver's side then pull down but it just won't pop off. I'm afraid that if I use a screwdriver to pry it down the tabs on the lens cover will break. Is there a trick to this? Dang, if I can't even change a light bulb how in the heck can I expect to fix the trunk problem.
Sorry it took a while to get back.
The trunk light cover can be removed by 2 clips on each end. You need to slide something small, like a tiny flat head screwdriver in the middle of the end of the cover and gently push and the lens will come off. You can use something like a flat metal finger nail file.
Here's an update. I was finally able to get the plastic lens off of the trunk lamp...as you said, I used a flat tip screwdriver to pry it down...it was in there so tight it came out to the point where I felt the plastic was about to crack.
I made some diagnostic progress...or I should say I learned of some weirdness. Here is what I found:
1. I purchased a brand new trunk lamp switch button and replaced it. It made no difference. Because the trunk lamp doesn't work I was never able to play with the trunk switch button and watch the trunk lamp go on or off.
2. I looked at the trunk lamp bulb. It's is fine. I took a resistance measurement to make sure it was not "open". It had a small resistance which tells me that if it got 12V it would light up.
3. I measured the voltage going to the trunk lamp bulb. With the trunk open you get a reading of 0.01V which is not enough to light the bulb up. Oddly, when you push the trunk lamp switch button in to simulate a "closed trunk" the voltage actually goes up to 0.11V. You also get a reading of 0.11V when you pull the trunk lamp switch button out which is supposed to turn the lamp out.
4. The rear seat dome light does not light up. I used the button in the overhead console in the front to try and turn it on. It never comes on.
5. I removed the bulb for the rear seat dome light and inspected it. The bulb is fine and would light up if 12V were applied. I checked the continuity and resistance as I did the trunk bulb and got similar readings. With the volt meter on the rear dome light fixture I observed 0v when the dome light is supposed to be off and 2.3V when the dome light is supposed to be on. It takes 12V to light the bulb properly so this explains why the bulb never comes on.
6. Here's my biggest discovery...when the button for the rear dome light is push "on" I experience the problem with trying to open up the trunk. What does that have to do with the trunk I don't know. Apparently, the dome light button has been on all this time but I wouldn't know it because the rear dome light never lights up. So, with the rear dome light button turned off I am able to use the FOB remote to open the trunk at will regardless of if the doors are open or closed. However, with the dome light "on" I experience the problem in my original post. One thing I should point out is that with the dome light off the center console switch still does not work regardless.
I feel that if I can solve the problem of the rear dome light and the trunk light I will make progress towards fixing the trunk opening problem. The question is: Why am I not getting 12V to either light when they are supposed to turn on? Is there a relay somewhere that controls this?
Last edited by SyberTiger; 05-28-2016 at 02:28 PM.
It appears that my suggestion at the beginning of the thread has opened a can of worms! Possibly ground connections? As you have tracked down a lot of the problem, maybe a shop need to look at it when you tell them what you found. If the FOB works, at least your in. I am stumped at this point?
It appears that my suggestion at the beginning of the thread has opened a can of worms! Possibly ground connections? As you have tracked down a lot of the problem, maybe a shop need to look at it when you tell them what you found. If the FOB works, at least your in. I am stumped at this point?
Unfortunately, the original poster on another forum who had the same exact problem never came back with the solution he found. I sent a direct private message to him but never got a response.
Okay...now that I was able to verify the problem wasn't the trunk switch button and performed the diagnostic work above it allowed me to move on to the electrical issues I asked questions about. When you determine that you are having electrical issues the first step is to check the relays and fuses. I checked the fuses first.
Kind of getting used to the weird German engineering on the car...I'm sure I'll never understand why Germans do what they do but anyhow, that's a long b***h session for a latter day. Anyhow, found the fuse box in the engine and also the one in the trunk under where the spare tire is stored. The engine fuse block didn't have a listing for a trunk light but it did for the rear dome light (only). Weird thing is they had the #9 fuse in the engine area listed along with the #2,#4 & #6 fuse in the trunk area as all being for the rear dome light. That must be one heck of a fancy dome light to need four fuses in two different locations of the vehicle! When I got to the #6 fuse which is a 5A fuse I noticed it was blown. I replaced it with one of the spares in the engine fuse block and voilà the rear dome light works!...AND the trunk light works...AND the trunk opens without a problem now! Interesting that you can leave the rear dome light on (now) and the trunk will open whereas when the fuse was blown leaving the dome light on prevented the trunk from opening with the key FOB.
The center console trunk release button still doesn't work but I'm going to assume it is worn out and needs to be replaced so I'll order a new one and hopefully I'll be good to go.
Last edited by SyberTiger; 05-28-2016 at 05:43 PM.
Glad to hear you got it solved. Removing the console is pretty fast to do.
The one thing you need to remember. as it's not very visible are the 2 screws in the ashtray. Open the ashtray, remove the tray, and on the sides are Phillips self tapping screws. Because of the angle to get at them, you may need a stubby screwdriver.
Glad to hear you got it solved. Removing the console is pretty fast to do.
The one thing you need to remember. as it's not very visible are the 2 screws in the ashtray. Open the ashtray, remove the tray, and on the sides are Phillips self tapping screws. Because of the angle to get at them, you may need a stubby screwdriver.
Thanks for the disassembly tips. Without taking it apart first can you tell me what the part number is for the switch? It appears that depending on the year build there is either an assembly shaped like a "U" which contains all the console switches or there's a single switch. I'm hoping that I only need to replace the one trunk release switch and not the entire "U" assembly.
Can you send a photo of the console area. The U can be disassembled once out, as it has clips around the edge. A lot of posts mentioned that people had spilled Pop or Coffee on the console in the past, and glued up the contacts. When you get it out, you can see if that may have been the case. Once I see the console, I can find the part number.
Disregard my post about the ash tray. The console just pops off. You need to remove the shifter knob, lift off the shifter plate (P,R,N,D). Open the cup holder, and push up on the console. Disconnect the wires under the console, and the U is held to the console with 2 sliding clips, one on each side.
Can you send a photo of the console area. The U can be disassembled once out, as it has clips around the edge. A lot of posts mentioned that people had spilled Pop or Coffee on the console in the past, and glued up the contacts. When you get it out, you can see if that may have been the case. Once I see the console, I can find the part number.
On the photo showing the shifter knob, the black piece below the tan knob is twisted, and then the knob can be pulled off and lift the burled panel to get at the U shaped switch holder underneath
On the photo showing the shifter knob, the black piece below the tan knob is twisted, and then the knob can be pulled off and lift the burled panel to get at the U shaped switch holder underneath
I finally got a chance to remove the U assembly. It looks like I have the "face lift" C230 model which has an integrated unit (not individual switches that can be removed). I can't see how you'd get the trunk release button removed. The link you gave me for the eBay trunk release button shows a different switch which has a "finger indentation" in the lower top portion of the switch. Note that in my picture there is no such indentation. On my model you are supposed to lift up on the front portion of the trunk release button to pop the trunk. I assume on the eBay switch you push down where there is a finger indentation? Let me know...thanks!
Have you actually removed the U from the car?
The switch is a rocker style switch, and the fitment chart indicated it would it.
Try to segregate the color codes for the switch and jump it in the harness, and see if the trunk will open>
Have you actually removed the U from the car?
The switch is a rocker style switch, and the fitment chart indicated it would it.
Try to segregate the color codes for the switch and jump it in the harness, and see if the trunk will open>
Yes, I removed it from the vehicle. I didn't take a picture of it but it is identical to the picture above. Note that this "U" is different that what most folks are selling or posting. The trunk switch is not a rocker switch on this vehicle. To open the trunk you lift slightly on the front of the switch. I couldn't figure out how to easily remove just the trunk switch on my "U". There's about 9 or so screws on the back of the "U" and I assume you'd have to remove them all to get access to the switches but then again, they just might be soldered on a circuit board.
There is only one way to find out. As switches are available, it is a clue that they can be removed. Give it a shot.
I haven't seen a single switch for sale which is the type on this "U". It is not a rocker switch. I was hoping someone familiar with this type of "U" would know without me having to take it apart and break it more than it already is. I'll try and get a better closeup pic of the switch and post it.
05-17-2016, 11:53 AM
Trunk opens intermittently on 1998 C230
