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…

Ignition Key OFF, Ignition Key ON and ENGINE RUNNING:

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$1350.00 is what the dealer is asking to replace the Instrument cluster on my 99 SLK 230.

I went to the dealer and had them replace both taillights (under a recall), check the transmission fluid level (car didn't come with ATF dipstick), requested the radio code and a full system diagnostic. I also requested a printout of the results.

There are a lot of codes there!!! Most say "STORED", and only one says "Current and stored", both on page 1. Interesting enough, instrument cluster on page 4 doesn't even show an MB number...

Need help understanding all the codes/info, connection between them. Where should I begin? Should I replace the cluster first? Can I get a used one or has to be a new one? Can an independent mechanic shop program it or do I need to go back to the dealer

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My first thought whenever I do something and it makes something else break I always go back and re-check what I just did to make sure it wasn't the cause. 99% of the time it is. I'd closely look at the plugs you disconnected and reconnected. Any chance you put one in the wrong socket or the wrong way? In the old days the plugs on the back of the clusters would have a center indexing pin. If that pin broke, which is often did, and you plugged the plug in even one pin off it would cause the kind of trouble you see. I'd say something you did caused this...either in the disconnecting and reconnecting of the plugs or in the solder job - make sure you didn't leave some solder loose on the board which is bridging across traces...all it takes is one small bit of solder to wreak havoc.

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Marty D.

2013 C300 4Matic
1984 BMW 733i
2013 Lincoln MKz