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SLK R170 230 - Will not start / Not cranking

20K views 21 replies 7 participants last post by  mchild 
#1 ·
:crying:Reconnected my fully charged battery yesterday after being disconected for a few weeks. Turned key to start engine but there is no cranking noise, not even a clicking noise. Could it be a problem with the immobiliser? Thanks.:smile:
 
#2 ·
fully charged battery? how old is battery? sometimes charging a brick will not turn it into gold :D

check condition of battery cables and ground
 
#4 ·
#6 ·
The starter is controlled by the cycle module N65, which is inside/under the fusebox in the engine compartment. There is a relay inside N65 for the starter. You can check the voltage at the diagnostic connector (the white connector inside the other box that's also under the hood) when cranking to isolate your issue. It's a VT/WH wire on pin 1 of the diagnostic connector. Look for +12V during cranking. If +12V is present during cranking, you likely have a bad starter or bad wiring to the starter.
 
#7 ·
Tbh, sounds like people are pointing you at more difficult options. Pick the simplest to disregard. I spent months figuring mine out & all it was, is a **** plug connection (green wire).

Look at that first, will take you less than 3 mins to absolutely confirm & then fix it or move on ;-)
 
#9 ·
Pasted from the Sticky: K40 relay module post.....

Mine (as mentioned before) has had the intermittent fail on the K40 relay. But i have since narrowed it down.
On the top of the K40 are a series of plugs, as you look at it in situ, the LH plug (black 4 pin) which has only 1 green wire going into it is now my culprit.
When it entered "Overheat" mode, fan going full tilt but not starting, i wiggled the plugs & the fan died off & car started. I then waited till it did it again & noticed LH plug was the culprit.
I disconnected this plug & tried starting & hey ho, it went into overheat! Plugged it back in after using switch cleaner & all is good.

So there you have it, a temp fix is wiggle it while fans spinning, then clean contacts for this single green wire to sort a permanent fix
 
#11 ·
When I turn the key there is no clicking noise from the starter. The engine fan comes on and stays on. The diagnostic machine is not getting any communication from the engine control unit. Checked the K40 relay but could not see any damage. Is it more likely the ECU gone bad or K40?
 
#12 ·
I'm sure I've read that engine fan coming on and staying on can be a symptom of bad K40 solder joint... apparently (never needed to do it myself as I have R171), you might need to inspect the K40 solder joints under a magnifying glass. If you confident with a soldering iron, may be worth re-flowing/soldering the joints anyway, just to be sure.

I've heard people say that jump starting a car can cause other issues, possibly with the ECU, but I don't know anyone personally that's had a car's ECU suffer because of it.

I'm sure others with R170 experience will weigh in again soon..
 
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#14 ·
"I'm sure I've read that engine fan coming on and staying on can be a symptom of bad K40 solder joint..."

Agree. This is a classic symptom of a K40 relay joint(s) failing. The bad solder joints can be very difficult to identify. My K40 went bad, albeit on a different part of the board with different symptoms. Re-soldering some of the joints fixed it for me and it's lasted ages since I did it.
 
#17 ·
#19 ·
The K40 relay provides power to the ECU. Now that you've seen the fan on - game over. Re-flow the solder on the K40, or just replace it (it's pretty cheap). Try cockneyricks solution too.

Don't rely on a visual check of the solder joints - you can't see the areas where the joints fail.

If you're not handy with a soldering iron, find someone who is, and have them re-flow it.
 
#22 ·
The K40 relay provides power to the ECU. Now that you've seen the fan on - game over. Re-flow the solder on the K40, or just replace it (it's pretty cheap). Try cockneyricks solution too.

Don't rely on a visual check of the solder joints - you can't see the areas where the joints fail.

If you're not handy with a soldering iron, find someone who is, and have them re-flow it.
as efair said . . .
 
#21 ·
As efair says

Don't rely on a visual check of the solder joints - you can't see the areas where the joints fail.
 
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