I’ve been having strange issues with the SLK230 since the day I got it. I’ve known about the P1235 OBD2 error code since I scanned it in before I got the car. Doing some research on the various forums and internet help sites I determined one of the areas to look into was the K40 relay module. This module is has been known to have failed soldered connections after a period of time. I removed it from the motor cabin and took it apart. The typical connections that fail didn’t look so bad but I went ahead and removed the old solder and flowed new solder for each known failed connection.

Once I put everything back together I reset the errors and rode the car for a couple of hundred miles. All seem to work until I got a full tank of gas. The CEL came on again and the P1235 code was back. During this time of failure the supercharger would be acting up too. Sometimes it would come on and other times not.