Join Date: Nov 2012
Location: Los Angeles, CA
Vehicle: 1999 SLK 230
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1999 R170 SLK230 Supercharger Issues - P1236 is ongoing, but P0410 went away after a K40 re-solder... Need help please!
Before anyone says "use the search box" - I have, extensively.
My problem has been going on over a year. It started with a CEL with the code P1236 (supercharger clutch) but at the time my supercharger was engaging normally (around 2200 RPM while in Neutral) and my MB mechanic told me the car had the right amount of power so it wasn't worth doing anything at the time.
Fast-forward to now and I have to get the CEL resolved in order to pass smog and renew my registration. So I started looking into the problem.
As of this morning, I had codes P0410 and P1236 showing. I revved the engine at idle and noticed the SC clutch was not engaging at all. Google and this forum led me to believe the K40 relay might be responsible for my problems, so I addressed that first.
I removed the K40 relay and resoldered the three solder joints in the upper-left corner. I couldn't remove all of the old solder so it's possible the relay still needs soldering work done. However, upon replacing the K40 relay I noticed both trouble codes had cleared (maybe due to the battery being disconnected?)
One of the other troubleshooting steps I noticed while researching a solution was to make sure the vacuum hose leading to the secondary air injection valve has vacuum pressure. I pulled the connector off the valve and immediately the line broke, which led me to believe a cracked and leaky vacuum line was partially responsible for my CEL. I put a finger to the broken end of the vacuum line and there was indeed negative pressure on the line. At this point, the CEL was still gone and I knew the secondary air injection only occurs on a cold start so I thought I'd be able to pass smog and deal with the vacuum line later.
At this point, I went to get a smog test. The CEL light stayed off for the 10-minute drive to the smog check place. During the test, the CEL came on again but this time only P1236 is showing up.
When I got home, I called my Mercedes mechanic and they gave me a new piece of vacuum tube that I used to replace the old broken line. I thought that would resolve my problem but it doesn't seem to have made a difference.
I have been reading a lot of threads about these two trouble codes and the SC clutch not engaging, and I noticed a lot of people who were able to connect their SC clutch directly to 12V in order to test whether the magnetic clutch is functioning.
My problem: I have no idea how to do this test myself!
If you know how to test the SC clutch, please describe it in detail or direct me to a link that describes the procedure. For the life of me, I can't figure out where the wires connect to the SC assembly.
In addition, I noticed the air bypass valve that connects between the air filter box and the SC is staying open no matter the RPM. I have a feeling this is related to the SC clutch not engaging, but I can't find any useful information on how to diagnose or repair these problems.
If you can walk me through a set of troubleshooting steps, that would be really useful.
One more note: it seems the fan in the box with the K40 relay and other electronics has stopped working. So excessive heat buildup may be what caused these other problems. Because the fan isn't working, I'm leaning towards it being an electronic problem rather than a mechanical one.
Any advice is helpful! Thank you!