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W202 c230 Sedan 1998
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Discussion Starter #1 (Edited)
My car stopped working out of nowhere the other day: doors don't open remotely anymore, windows don't roll down and the radio doesn't turn on. Dashboard and headlights turn on, but no crank when I turn the key. The battery level seems fine when I tested.

I searched the forums and thought it might be a bad K40 relay. I looked at it today and I'm not sure. I attached two pictures -- what do you think? The discoloration looks lighter than what I've seen on the forums...

Thanks for helping out a poor grad student!

edit: it turned out to be the battery after all. I didn’t measure properly. I’m still glad I opened up the relay, the pins seem to look like they can use refreshing.
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1995 C280 (165K mi)
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It is hard to say from the color. But the 3 solder points do look a little burned. You should look at it from the side under magnification.
 

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Discussion Starter #3
Thank you! I will go ahead tomorrow and take a picture from the side. Below is another close up I took today. They do look a little weird. Not sure if it’s enough to cause trouble
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W163 and General Mercedes Host
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Prior to this stage (which would not be my first initial inspection), have you scanned for codes?
What did you do prior to this stage of inspecting the K40?
Checked fuel pressure at the rail?
 

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W202 c230 Sedan 1998
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Discussion Starter #5
I haven’t scanned for codes, will do tomorrow. I also haven’t checked the fuel pressure.
 

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I haven’t scanned for codes, will do tomorrow. I also haven’t checked the fuel pressure.
Scan and post any saved error codes here.

AND when was the last time you changed your fuel filter? possible clogged FF.

As for the K40, if it IS the K40, you may be able to salvage it by re-flowing the solder at those 3 joints. Hard to say based on the color of the CB at those locations. Hit and miss on the reflow of these K40 issues. I would at least scout around for a replacement K40 relay while you perform these other checks.
 

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W202 c230 Sedan 1998
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Discussion Starter #7
I bought the car last year and haven’t changed the FF myself. Couldn’t find any note about it in the repair log. Only this repair note from two years ago, but not sure if it’s related.

The car definitely did show signs of a clogged filter, like stuttering when starting etc. But would a bad FF also cause the doors and radio to stop working?

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I bought the car last year and haven’t changed the FF myself. Couldn’t find any note about it in the repair log. Only this repair note from two years ago, but not sure if it’s related.

The car definitely did show signs of a clogged filter, like stuttering when starting etc. But would a bad FF also cause the doors and radio to stop working?...
This has nothing to do with the radio not working.
What do you mean by the radio not working? It doesnt turn on? or radio AM/FM reception? or something else?

What do you mean by "doors not working"?
You need to explain more clearly rather than using general broad terms for both these issues - "not working" isnt clear enough.
In future, one topic/issue per thread.
 

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W202 c230 Sedan 1998
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Discussion Starter #9
Thanks, will make sure to explain more clearly and keep it on topic.

I first noticed the problem when I couldn’t open my car with my remote Key fob, even though I bought new batteries earlier. So I have to use the metal key to open the car. The radio also seems out of power, it doesn’t turn on.
 

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Thanks, will make sure to explain more clearly and keep it on topic.

I first noticed the problem when I couldn’t open my car with my remote Key fob, even though I bought new batteries earlier. So I have to use the metal key to open the car. The radio also seems out of power, it doesn’t turn on.
1) Lock or unlock or both - with the fob do not work? Is the issue only with the front DS door or centrally?
2) Radio - "seems" to be out of power? too vague....Either it does or it doesnt. Do you get reception? Elaborate in detail
 

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W202 c230 Sedan 1998
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Discussion Starter #11
1) None of the buttons on the fob do anything, I can neither lock nor unlock. When I open the front DS door manually with the metal key, only the front door unlocks. Every other door stays locked. I do have a “panic” button on the key - can the problem be connected to the security system?

2) The whole car radio unit does not light up, even when I turn the key and my dashboard lights turn on. I made sure to push the on/off button on the radio unit but nothing happens. I don’t even get to check the reception, or use any other feature of it.
 

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Please update your user cp info:
click on your icon----> click on Account Settings---->
goto Account Details----> add vehicle details---->
add your make model YEAR ----> click save
 

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W163 and General Mercedes Host
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1) FOB - check/replace the FOB batteries. Check to see if the infra-red light displays when you press the button(s) aimed at the car. Also, possibly, the FOB is damaged and you may be able to repair it.

2) Check your fuse box. There are 2 - one under the hood, DS. and one in the trunk, under the deck cover, at the back. ON the backside of the lids, the fuses are listed. Look for the window controls fuse and check to see if it's good.



Reset all windows.

3) Radio - check the fuses first. If fuses are ok, you may also need to check if power is reaching the radio. You will also need the radio code (if it's an oem MB radio) to activate it (anti-theft system) Radio code may be written on the radio body itself. If not, there will be a serial # on it, call your local MB stealership and give them the serial #. They will provide you with the radio code specific to that radio that you can input to activate it.
 

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Discussion Starter #15
1) I checked the key, infrared is working and batteries are new. I have a second key that also does not work anymore, so currently I doubt that it's the FOB.

2) and 3) will check the fuses.
 

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1) I checked the key, infrared is working and batteries are new. I have a second key that also does not work anymore, so currently I doubt that it's the FOB.

2) and 3) will check the fuses.
Have you tried resyncing the FOB(s)?

Also refer to your owner's manual on the exact procedure

 

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W202 c230 Sedan 1998
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Discussion Starter #17
So, today I did the following:

1) ran the diagnostics, no codes displayed

2) resynched the FOB - still doesn’t turn on or open via remote

3) Checked all the fuses under hood and in the trunk. They all work, including the ones for radio.

3) Checked the fuses on the K40 relay. They all work except for the big yellow 40 fuse. I changed the fuse, it didn’t work. I put the fuse in another box, there it did work. So the fuse seems to be alright - but the slot on the relay doesn’t.

Is this a sign of a bad relay?
 

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So, today I did the following:

1) ran the diagnostics, no codes displayed

2) resynched the FOB - still doesn’t turn on or open via remote

3) Checked all the fuses under hood and in the trunk. They all work, including the ones for radio.

3) Checked the fuses on the K40 relay. They all work except for the big yellow 40 fuse. I changed the fuse, it didn’t work. I put the fuse in another box, there it did work. So the fuse seems to be alright - but the slot on the relay doesn’t.

Is this a sign of a bad relay?
1) you scanned at the 38pin under the hood or at the obd2 port under the steering wheel for codes?
These older MBs need to be scanned at the 38pin (your scanner needs to be a better one to read specific error codes, if any, from here)

2) tested both FOBs? Sounds like your fobs are toast, but possibly repairable. You need to dig a tad deep a tad deeper...


OR


3) For the radio, you've made sure you pressed the LS power button? If so, and no powercomes on, you need to pull it our with a set of "keys", as shown or make a set with credit cards, then test the 12V line (possibly red or pink) for power with key in ignition, position 2. From the fuse to the radio, you're possibly not getting any power or the radio is dead (check fuse on back of radio, if any)

Screen Shot 2020-04-05 at 7.13.36 PM.png

4) Sounds like the k40 issue, that is typical with these -
 

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Discussion Starter #19
Solution: it was the battery after all. I had to call roadside assistance that did a better job than I did before. Still glad to have looked into all these different issues, at least now I am prepared if the K40 ever fails. Khomer, thanks for your advice!
 

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Discussion Starter #20
In addition -- and on topic, after all: even though my car works, the 40A maxi-fuse on my module still doesn't wor. Does anybody know what it's purpose is? Do I need to worry about it? I tried to re-solder the pins that looked bad, but I didn't get the fuse to work.
 
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