Mercedes SLK230 K40 RelayChances are if you found this page you’ve encountered the dreaded Mercedes-Benz SLK 230 K40 relay problem. For those of you that are not familiar with the K40 Relay, it basically controls throttle response, fuel management, and your fuel pump. I also read some where that it has something to do with emissions, I’m not 100% sure, but I do know how to fix it!

You’ll know if you have the K40 Relay problem by the following symptoms:

  • Your car is not running great, the throttle is not responsive
  • When you turn the car off, you smell the faint smell of gasoline
  • Your check engine light is on
  • The error codes causing your check engine light are the following: P1235, P1236, P1420, P1525 (you need a code reader to determine this)

The bad news is that if you are to take your car to the shop to have this fixed, the part alone is several hundred dollars plus the labor for them to repair it and you’ve got yourself one expensive problem. The good news though, is that this problem is relatively easy to fix if you know how to use use solder and a soldering iron.

I have successfully repaired this on my own 1999 Mercedes SLK230, and it took me under an hour to do. It’s really not that complicated. The tools you need are:

  • Phillips Screw Driver
  • Small flat head screw driver
  • Soldering Iron
  • Solder
  • Your hands and a little patience

Fortunately for you, I have step by step directions on how to repair the Mercedes SLK230 Relay problem in my photo gallery. Give it a visit and you can save yourself several hundreds dollars by doing it yourself!