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Early SLKs suffered from soldered joint failures on the K40 pcb. This mainly affects smooth op and fuel pump.

I have just repaired mine.

K40 Relay - Right hand drive

LHD opposite

Remove neg batt term
Remove computer lid
Unclip holding tang and lift up module
Pull off connectors
Open case of module
Inspect soldered joints for cracks, overheating, dry joint etc
An eyeglass may help (top left hand group of three)
Remove old solder and resolder with new
Replace module
Push on connectors
Remove and replace 40A fuse to wipe the contacts.
Replacelid
Replace neg batt terminal.
Start car

Redo radio code if required.

more: http://www.benzworld.org/forums/r170...ssociated.html

Bazzle
 

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Yeah...it's a keeper. The post that is. :D Thanks Bazzle!
 

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WOW! Even though I'm not a R170 owner, I like to read the how-to stuff just for general knowledge. Thanks Bazzle. Y)
 

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So was there a cold solder joint there? I don't see one. Or was the picture totally to show how to get to it?
 

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More good info from Bazzle!!!

Hope I never have to do this. Yikes!

SLKman:tu:
For some its fun! The best part of the troubleshooting procedure. For bench technicians, soldering is like...landing for pilots. Oh wait...I get to do both...woohoo!! :rb
 

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Just for you Mtiede :bannana:

Bazzle
Thanks for the close up. Looks bad to me :)

Reminds me of the time I built my first TV. It took me 2 weeks to solder all the pieces on the circuit boards and 2 weeks to find out what was wrong :)

Turned out they gave me a wrong part and smoke and sparks came out of a resistor when I turned it on. After I got that figured out, then it took me a while to find a coil with a broken wire. After than it ran fine for about 10 years.

But I did my fair share of soldering and looking for those cold joints.
 

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Hey Bazzle thanks for the post.
I had trouble starting my 2000 SLK 230 yesterday. When I turned the key to start, I got all the idiot lights and the radiator cooling fan was running in high speed. The engine was warm but not hot. The car did not crank the starting motor at all. I checked and it did not set the check engine lightl. A couple hours later I tryed to start the car and it started right up normally. I thought that the problem might be in the ignition switch or the starting motor/soleniod.
I found your post and decided that I better check it to see if that was the problem. Did you figure out what the cold solder joint controlled?
I took pictures of mine and they look identical to the pics that you posted. SO this problem is not unique to your car. If that is not the problem I will pull the starter/soleniod and then check it. There was no noise except for the radiator fan when I tryed to start it.
 

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My 1999 SLK230 Has Had A Rough Idle For A WHILE Now, More So In Reverse. Dealers Have Said It Was JUST A Vacuum Leak And Could Never Narrow It Down/Too Many Vacuum Lines. Car Has Also Died Out A Few Times And Wouldn't Even Crank Over After It Dies Out. The Car Failed Emissions Test Last Month. The Codes Showed A Throttle Position Switch Learned Open/Replaced That No Luck. A Fuel Pump Circuit High and Secondary Air Valve Code, And Many Other Pending Codes. I Don't Trust Any Of The Local BMW/Mercedes Dealers In My Area. They've Lied And Taken Me To The Bank Before. I Usually Fix My Own Cars But This One Stumped Me. I Didn't Want To Throw Parts At It. Today I Took It To My Local Private Shop I Know And They Said It's Probably The K40 Relay. Just Like The Post Said. I'll See If It Works.
 

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Happy Holidays everyone!

If your SLK230 is over 5 years old, it would be WELL worth the $170.00 US to just replace the relay unit as a preventive measure. The part is not that expensive and it's a cake walk to change out. No one likes to be stranded miles away from home! PLUS, it may take your dealer time to order one. You will be down for that long. I lucked out and got the LAST ONE my dealer had!

REMEMBER: A smart one learns their own lessons, a wise one learns lessons through the lessons of others, and not-so-smart one NEVER learn any lessons...

'Tis the season to be a "wise one", isn't it? Hehe
 

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Thanks for sharing your knowledge Bazzle. Also a big thanks for taking the time to document with pictures.


:Beer:
 

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My 1998 slk230 just started symptoms of k40 relay issues. The dash lights come on and when I press the throttle, the engine does not respond although it is still running. Then, the dash lights go out and everything is back to normal. Just had the Benz dealer diagnose and they said it is a bad k40 relay. I checked the k40 relay board described in previous posts, and the soder points are clean and solid. Is the actual k40 relay on the other side of the engine compartment(drivers side)? The sealer also had "discs" listed under parts. Not sure what that is. Anyone have any knowledge of replacing the k40 relay itself, and what "discs" are in relation to the k40?
 

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K40 relay or K40 relay module?

Just searched the net for a k40 relay for my 98 slk230. I found what appears to be a k40 relay, but not the k40 relay module described in previous posts. Both part suppliers said it is located "right front under hood", but I don't see anything that looks like the picture on their site. Does anyone know anything about the k40 relay itself and where it is located? Or do I need to just be concerned about replacing the k40 relay module described in the previous posts?
http://www.autopartswarehouse.com/search/?N=11245+1668+4294967269+5866
 

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Does any one have the diagram of the K40 realy board? I need to find out which realy is feeding the fuel pump to install an additional relay to cut it off!
Thanks
 

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I have found that this relay board is responsible for 2 failures for my mercedes



1. Check engine light error codes -
p1235, p1236, p1420, p1525 (Rightmost circle in attached image)


2. Failure to crank - intermittently (Center circle in attached image)

I am including the close up from another post showing the bad soldering points. Make sure that you solder all 3
 

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