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DISCLAIMER: My SDS is broken, so while I wait on repair, I am trying to troubleshoot this the good old way
What causes clutch not to engage? at all, I dont mean loosing boost because of heat soak, I am talking about ECU not ordering the clutch to engage at all...
12V is present at clutch connector.
ground line continuity from clutch connector to ECU is OK
introducing ground at ECU pin1/connector1 engages the clutch OK
So the problem is logical; the ECU is deciding not to engage the compressor for some reason.
IAT is within normal range.
What else can be messed up causing ECU to disable the compressor?
I had intermittent (and finally , none at all) SC clutch engagement when my bypass throttle (on my 2003 sl55) was failing (m16/7 recirculated air flap). It did throw codes in my case.
I printed you the page from the Mercedes WEB ETM that gives an overview of the inputs associated with the SC clutch .... hope that helps.
I had intermittent (and finally , none at all) SC clutch engagement when my bypass throttle (on my 2003 sl55) was failing (m16/7 recirculated air flap). It did throw codes in my case.
I printed you the page from the Mercedes WEB ETM that gives an overview of the inputs associated with the SC clutch .... hope that helps.
Cheers,
Chris
I was reading this publication yesterday, and voltage did drop, due to discharged battery when the issue first happened. but SC never came back after batteries were recharged.
I tried to disconnect both batteries, wait for a bit, and reconnect, no luck.
Expensive experiment, try replacing the battery? Or IAT sensor is also very cheap and worth doing if it hasn't been done for a while. Not that I advocate throwing parts at a problem and hoping for the best of course.
Expensive experiment, try replacing the battery? Or IAT sensor is also very cheap and worth doing if it hasn't been done for a while. Not that I advocate throwing parts at a problem and hoping for the best of course.
all of these components are passing tests, battery voltage on both batteries is >12.5, MAP and IAT both reading normal range of vacuum and temp.
Did you check your IC pump relay too? The fuse is position 4 and the relay is the very bottom one on the same module. It's a skinny one with a fat one directly above it. See pic, green arrow
This was my issue, someone had misplaced that relay when troubleshooting the fuel pump and put it back in the wrong spot. I had exactly the same symptoms as you.
Did you check your IC pump relay too? The fuse is position 4 and the relay is the very bottom one on the same module. It's a skinny one with a fat one directly above it. See pic, green arrow
This was my issue, someone had misplaced that relay when troubleshooting the fuel pump and put it back in the wrong spot. I had exactly the same symptoms as you.
You placed me on the right track!
in my case, the whole issue started similar to your, dead M3 fuel pump. Replaced fuel pump, still intermittent pump run.
Finally it turned out to be a bad wiring, near the M3 fuel pump, and N118 module. fearing corrosion and future problems, I opted to bypass the wire completely, and run a new one from the fuse box K40/5 to N118
Turned out the the bypass i installed left Z3/29 without power, and subsequently K27/5 relay without power...
Low and behold, without power to K27/5, the car runs, but no boost...
According to STAR, K27/5 powers primary fuel pump inside the tank, however, SL55 has only one external pump, so I am guessing K27/5 powers the M44 coolant pump, thus no boost without K27/5
Good news is if I keep the car for 15 more years, and my son wants to take it for a ride, I discovered an easy method to tame down the 600HP monster down to 230HP grocery getter, just replace the K27/5 relay with a dummy one... LOL
That makes me want to wire up a valet switch for when my wife takes it for a spin. Last time she drove it she used up like half my tires, came home with a smile on her face though. It was brutal chasing her down with the Tahoe full of my kids as she did serpentine patterns every time she stabbed it from a stop.
08-22-2017, 01:23 PM
I had exactly the same symptoms as you. 
