'98 C280 Power seat problems
 

I have used the search feature and have not found any info that can help my present situation.

Here is my Problem.

For about 2 years now My powers seats have been getting worse in my C280

first they would only work after the car was started and running for 10 minutes but would work normally when I openned the door.


Now sometimes they don't work for days at a time.

I beleive it is a power supply problem of some sort because they either work at the same time or they are stuck at the same time so it is not the switches.


Is there control module for the seats that might be going bad (if so can someone tell me the location of it in a W202 chassis.

Could it be a relay that needs replacing. It is very annoying when you want to move the seat for whatever reason but you can't.


Help a brother out.

98 C230 Both Power Seats Inop At Times
 

Hi Smartkey, My wife has been telling me for the last few weeks that the power seats in her 98C230 are inoperative at times. Checked them twice & they were workng ?? Comes home from the grocery store yesterday ,seats not working. Grab my digital volt meter & checked across seat fuses on under hood fuse panel,all OK. Fuse panel cover panel says there are related fuses in trunk.Removed trunk floor trim ,all fuses OK .Don't know where the seat relay is located . I suspect an inter- mitent connection , see 2 relays under a black plastic under cover with 3 fasteners & remove panel. Wife is turning key on & off while I listen & feel for relay click. One relay is mounted vertical & the other horizontal.Checked the one left (horzontal),have 2 input BAT volt- age readings for power feed & coil feed & relay is clicking ,trigger circuit OK. Check output on 12 guage Pink/white- BINGO - NO OUTPUT Remove relay cover,check contact points for continuity with ohm meter & then under duty load for current flow.Both tests OK. Check solder connection to circuit board with a magnafying glass on the output pin. There was a small circle crack in the solder around the pin. Cleaned up the old solder & resoldered the connection & it's operating as designed. My Motto "Repairs though testing " ---- Ray

Ray,

That is pretty good for a first post!! I have high hopes for you. And since I have that exact problem (among many others) can you please confirm that the board you repaired was inside the relay? Or was it some other board?

Thanks,

Mike

Hi Mike,---- Yes ,it is the small circuit board inside the relay. Once you remove the relay cover by sliding 2 small screwdrivers along the 2 release tabs, the cover will pop off. Circuit board is attached at right angle to base containing the male pins. If you have the patients & soldering skills with a small soldering iron ,it's a piece of cake job,& will save you some bucks, you won't have to replace the relay. I have been an electronic technician for over 40 years , sorry to say not at a Mercedes Shop. Own 2 Benz only because I can tinker with them, now that I am retired. Let me know if you need more help. Ray

Hi Ray,

I have been an electronic tech for 17 years, so you have a few years on me!! Just fixed the GF's Sony last week. Anyway, this will be the second bad solder joint I have fixed in this car. First one was the headrest motor which I detailed in a previous post. I have to admit I found electrical problems in my Toyota also, but never bad solder joints. Don't want to talk about the FIAT......

You will find many interesting electrical problems presented on this site. But often the tribal knowledge goes farther than electrical knowledge in fixing them!

Mike

Hi Mike,----- When you remove your relay,you will see it is made in Austria , I think it is expensive to replace because of the components on the circuit. My opinion is the pretty looking shallow solder connection can't handle the current flow after many years of operation, plus heat,cold & vibration. I built up the solder wider & higher ( ^ ) to carry the amps. Time will tell ,but I think it will hold up. Ohms Law will determine if it can handle it. ---------- Ray

relay
 

during the daily work at the shop, i have seen several 202 chassis with the problem you describe, i have traced many to the relay in the trunk under the plastic cover.

This sounds typical of what I have seen on single sided circuit boards. The holes are not plated through so the solder joint is very weak. Thermal cycling in particular will cause the circular crack you describe. I have seen this often in TV's, on boards with hot devices on them. I suppose vibration might cause a similar problem. I wouldn't think that relay would run that hot with intermittant use. Not sure why they put that circuit through a relay anyway. Maybe that other circuitry in the relay runs hot for some reason.

Mike

Thanks
 

Hey today I open my email to find a link to old post. to find out that people have replied to it. Whenever I checked it there were not replies.

My mechanic replaced to relay for me and everthing is working again like it was.

Add one more W202 to this exact same problem (a 98 C280). I guess it is soldering time.

And yet another... 1998 C230, 70K miles.

and you guys come through again. Just fixed my c280 with the same resolution. 142K miles. :)

Thank you. Another 1998 C saved... 52K

Finally found it, YeeeHawww
 

I finally found k24 (convenience / comfort relay ) in the last square inch of my 1998 C230 that I hadn't stripped apart yet. Lo and behold the circuit board inside the relay had 8 out of 23 solder connections cracked (ring cracks). Will fix tomorrow and take pictures of the problem. I will try to post the pics. Thanks to everyone above and throughout the archives for helping to lower my aggravation quotient.

MattG
98 C230 first and last 55k miles

Pre solder pics of the convenience relay module solder cracks
 

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