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The supercharger on my 1999 SLK230 stopped working and my OBD II reader showed P1235, P1236, P1420 and P1525 codes. Thanks to this and other forums I was able to narrow it down to K40 relay (THANKS, I REALLY APPRECIATE ALL THE VALUABLE INFO!!!).

Two days ago I disconnected the battery (negative terminal) and removed the K40 Relay. Sure enough I found a bad/burnt connection and re-soldered it. Today, I re-connected all plugs to the K40 relay and re-connected the battery. When I sat inside the car I noticed the lights illuminating the clock, mileage and outside temp being “ON” (please see attached pics) and heard a continuous “beeping” coming from the dash. Gas gauge and engine temp needles DO move and stay at different position every time.

I started the engine and it runs fine. No “Check engine light” and no fault codes on the OBD II reader. Air pump engaged right away and it stayed on for some time. No RPM gauge readings. I took the car for a ride and it seems to be running great – supercharger kicks in, even though I can’t tell at what RPMs. No speed reading either…

Any ideas? Is there anything I need to reset after I re-connect the battery? PLEASE HELP… :confused:

Ignition Key OFF, Ignition Key ON and ENGINE RUNNING:


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