[Randino]

My wife was driving home tonight and the car stalled while she was turning right. No warning, no hiccup, just a quiet stall. She was actually at a red light, made a right turn and the car stalled 1/2 way thru the turn. The radio kept playing, the lights stayed on, the a/c fan kept blowing, just no engine and every warning light on the dash board lit up, as you would expect. When she tried to crank the engine she had nothing; not even a click as if it had a weak battery. I got there and tried to start it; wiggling the shifter in case it was a safety interlock; nothing. We pushed it out of the street, and checked the main fuses. I was able to pull fuse #11, ignition coil, and it was fine. I stuck the fuse back in. As we were getting into my car to come home I tried to start the SLK one more time and it fired right up. She drove it the rest of the way home.

What happened? How do we prevent re-occurance?

The battery was replaced this summer; it is strong, fresh and working fine. Not a bit of corrosion on the wires. Also, the lights, radio, worked fine thru out.

 

[Ryououki]

Sounds like it may be fuel related. Have you checked the K40 relay and verified you can hear the fuel pump moving fuel when it was not starting up?

 

[Randino]

when I say it wouldn't crank, I really mean we had nothing. It was as if a safety interlock was preventing the ignition switch from attempting to activate the starter. The CEL has not come on.

 

[Subby_]

sounds like the "crankshaft position sensor" (CPS). this will make the car stall and sometimes do intermittant start. it may or may not throw a code looks like its on the way out.

easy to replace and not expensive. its located at the back of the motor where it joins the transmission. can search on here how to swap out. 10min job at most

 

[Ryououki]

With 0 cranking, I agree with Subby.

 

[Randino]

Here is an update. I had AutoZone scan for stored codes, and the car had nothing to display. I went ahead and replaced the crankshaft position sensor this morning. Like you said, 10 minutes. In case anyone else searches, that screw head is an "E8". I borrowed the socket from a friend.

Hopefully we have fixed the problem and I'm not headed for issues with the K40 board.

Time will tell.

Thanks for your input.

 

[PetesPonies]

Mercedes ignorance here for me, but not general auto ignorance. That said, when a crank or cam sensors goes on "other" engines, it has nothing to do with the engine turning over. It has everything to do with the ignition system working; no start. Not spinning the engine over is a starting system problem. Not sure why or how those two systems would be interrelated. Again, this is from my knowledge of "other" cars, not Mercedes. Since most manufacturers actually run very similar computer systems, is there really anything different about the way Mercedes does this? If not, you may still have the problem.

 

[Kobus]

On Mercedes the engine will not turn over with a bad crank sensor - at least not on the M112 & M113 (V6 & V8).

 

[PetesPonies]

There is no signal being generated by a crankshaft not spinning. The trigger or reluctors that a sensor is "noticing" happen when they break the magnetic field of the sensor. When the crank is stationary, nothing is happening. Only thing that could possibly be sensed is an open circuit of the sensor, not sending the reference voltage back to the computer. Just doesn't make any sense to me. Any technical data of proof ?

 

[Randino]

I agree that I am skeptical that a bad crank position sensor could result in the engine not spinning at all, but it is an easier fix than the K40 soldering mess that seems to the next item to work on. So far, we haven't had any repeats of the stalling, but it has only been 1 1/2 weeks since the initial occurance. I don't know if this clue may help with the diagostics, but Holly does recall that the engine cranked "longer than normal" the day before it stalled. Since the replacement it fires right up. We use the auto start feature. Again, Thanks to all who contribute.

 

[cacecef]

Petes welcome to the forum. This is mostly a group of individual owners who help each other with problems that occur to all of us from time to time. A lot of experience with over 13 years of slk ownership is here in the stickies. Sometimes more than one answer can be correct or not. If you doubt something and want tech data or proof sometimes the poster will provide it or it has been provided before in other post. We just try and make the expense of mb ownership a little easier. Otherwise, it is up to you to remedy the problem yourself or go to the dealer or independent mechanic and let them fix your problem, ease your mind, and lighten your heavy billfold.

 

[Kobus]

. Sometimes more than one answer can be correct or not.

And Pete is correct in his reasoning. And I'm correct in my statement.
It depends on the type of error in the KPS (CPS). If it can be detected electronically, the engine will not turn. If it cannot be detected on key position 2, e.g. incorrect clearance between between pickup and the flywheel/interrupter, there is no static method to detect this and the engine will spin quite happily.
The first type will normally set a code, the second type may or may not set a code.