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Discussion Starter #1 (Edited)
Sorry, I know this subject has been beat to death but I didn't find any threads discussing my particular problem. The clutch engages during cold start for 60-90 sec like it's supposed to but never disengages like it supposed to below 2k....basically runs all the time (unless I unplug the round connector).

The car is not responsive and has little power so I'm guessing the bypass valve is staying open all the time but I haven't verified this. It throws P1236 & P0410 codes. I bought the car with this issue so I don't know what kind of power it should have but I would expect more than it does. It has 116k. Any ideas??

***UPDATE*** Wow, I guess not too many tech folks on this site or they are all tired of talking about this problem. I'll just document my troubleshooting method in hopes someone else may benefit.

So just turning on the ignition with the car not running engages the s/c clutch. I'm thinking a transistor in the ECM but I don't have a schematic. Because of the current that the clutch coils draws, there has to be a transistor/power amp being driven by a control signal. My experience with these is they will fail "shorted".

I don't suspect the K40 relay module since they are mechanical relays and they usually fail open (I checked anyway to make sure no contacts were stuck shut). From what I've read, the relay supplies the 12v to the coil and the ECM grounds the return....just need to trace that back thru. A schematic sure would help.

Rob
 

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Discussion Starter #3
OK no real updates here since I haven't had time to work on it. The car is coming off the road for the winter next week so I'll dig into the ECM then. That way if I blow something I've got a few months to fix it.
 

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Discussion Starter #5
I got a chance to open up the ME-SFI (ECM) to see if I could trace conn K, pin 21 to the bad transistor. Unfortunately it's a multi-layer board and is impossible to follow many of the traces so I'm stuck again. If anyone has a schematic for this that would be super!

I've attached a few pics of the board.....and yes the car still runs after putting it all back together.

Rob
 

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Discussion Starter #6
P0410 code gone...

I was able to eliminate P0410 by replacing a split vacuum hose going to the air pump switchover solenoid valve. Eventually I will replace all vac line tubing....especially the hard plastic ones which are brittle and break very easily. Since I can't troubleshoot the EMU any further (without a schematic), I checked to make sure the clutch coil wasn't shorted to ground on the return side and it was fine. Getting about 4.0 ohms across the coil so that's fine. :Beer:
 

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Any luck with this?

Hi Barchetta. I have the EXACT same situation with my 99 SLK230. Any luck so far?

Clutch checks out good. I too suspect the ECU. I have eliminated the K40 as a possibility (it seems to supply the + voltage, while the - connection on/off is controlled through the ECU. Like you, I took my ECU apart. Don't see anything burned. I agree...an ECU schematic would be great!
 

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Discussion Starter #10 (Edited)
Hi Barchetta. I have the EXACT same situation with my 99 SLK230. Any luck so far?

Clutch checks out good. I too suspect the ECU. I have eliminated the K40 as a possibility (it seems to supply the + voltage, while the - connection on/off is controlled through the ECU. Like you, I took my ECU apart. Don't see anything burned. I agree...an ECU schematic would be great!
Hi Katz,

Check out this thread on BenzWorld for updated info on this issue....I've been working with a chap from the UK on this.

http://www.benzworld.org/forums/r170-slk-class/1684378-supercharger-fault-help-please-2.html

I've found that SLKWorld is more geared towards folks that enjoy polishing their cars and doing cosmetic upgrades. BenzWorld has more tech savy folks that like to dig in and troubleshoot problems vs. going to the dealer or an indy for repairs.....just my opinion though. :burnout:
 

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Hi Katz,

Check out this thread on BenzWorld for updated info on this issue....I've been working with a chap from the UK on this.

http://www.benzworld.org/forums/r170-slk-class/1684378-supercharger-fault-help-please-2.html

I've found that SLKWorld is more geared towards folks that enjoy polishing their cars and doing cosmetic upgrades. BenzWorld has more tech savy folks that like to dig in and troubleshoot problems vs. going to the dealer or an indy for repairs.....just my opinion though. :burnout:
Thanks, Barchetta. Great information! Looks like I should also join BenzWorld.

I suspect that I will need to go the same route, since F21 is constantly grounded. The thought of doing ECU repair is a little scary, but since I managed to open it up and then reinstall it with no problems, I feel a little more confident about that.

It will be interesting to see if this repair resolves the issue for you. It certainly sounds like you are on the right track. Best of luck!
 
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