The K-40 relay is by the battery in the plastic case. Four phillips screws hold the cover on remove the cover and the relay it the first one closest to the drivers side it has all the fuses in it. DON"T FORGET TO DISCONNECT THE NEGITIVE BATTERY CABLE BEFORE STARTING!

 

Almost a week now and our 230 has not stalled! The K40 it was indeed! And thanks scrmnss for the relay location info! I'll be passing it on ...

Happy holidays everyone!

Jim

 

Should have said "almost two weeks now"! How time flies, eh!

Jim

 

Question please.
Looks like the K40 was the problem.
Did you change it or resolder?
When you inspected the k40 did you actually see a defect or did you jusr resolder one or all the joints just because that is what you were advised.
Another post has a similar problem but close inspection of the k40 shows no evidence of a dry joint.
What exactly was your symptom.
Stall when cold or hot or both?
Occasionally or always?
In anticipation of your response.
Do you mind sharing your VIN number? If not please advise.
Stuart

 

Taking mine to the shop now. Wish I had the soldering tools to do this myself alas, I do not. I will update if mine is the K40 relay as well. Seeing as mechanic "guessed" and replaced crank sensor already and problem still exists, I'm hoping we've spotted the culprit.

 

OK, never went to the shop. After watching the YouTube video. decided to try myself. UNHOOKED THE NEGATIVE BATTERY TERMINAL. Yanked out K40 Relay, saw no sign of bad soldering, cracking or anything. Looked new. Decided to take a chance and went to pick up a new OEM K40 relay from Mercedes (They also called it the Voltage supply Unit). Part # for my 1998 SLK 230 is A 210 540 00 72. Cost $204 with tax here in Orlando, FL. came home, swapped out the unit. Fired right up, running smooth. Hopefully it will continue to run without fault from here on out. I will keep you apprised. Thank you Bazzle and all of the other wonderful contributors on this forum. You just saved me $150 at least and day in the shop.

Disclaimer: I am no auto mechanic - this fix was SUPER simple.

 

OK, so far I'm feeling the love from my old benzie. Since swapping out the K40 she's been running great (knock on wood) Been a week, no stalls, no refusing to turn over. Before this was happening almost daily. Mercedes told me that if I put in the new K40 and it didn't work I could return it for a refund, so keep that in mind folks.

 

Still running strong

 

Hello all... am new in this forum and its really great to get vital info like this in maintaining the car... I bought my slk230 1999 model on dec.2012. Its got 58t kms on it and its been stalling past couple of months. I followed the directions on the K40 re-soldering. I also found a video on you tube. As I restarted the car, I was surprised that the auto-choke worked! Idling improved... as though the engine is more stable... Hope this fixes my problem of stalling. Thanks all for the tips.

 

Hi all... Just an update on my K40 works! After the re-soldering, the cars engine performance gravely improved. However, something new developed. Once I turned off the car, it would not restart!! Would have to let it cool down for a long time before restarting. My remedy was to bring down the K40 relay box and using a #1000grit sandpaper, I patiently sanded each contact point of the relays. There are a total of 5-relays and 10contact points. After that, all the problems were gone!! Even my aircon blower now turns on instantaneously the moment I turn the switch on the dash (previously it would turn on; but, very slowly). The car now restarts every single time, the engine performance is great! Definitely worth the time to this as part of a maintenance program (sand down the contact points).