SLK 280 Wont start

Discussion in 'Engine' started by portzy, Dec 13, 2015.

  1. portzy

    portzy MB Enthusiast

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    Hi. A couple of days I attempted to bring my SLK out of its slumbers to find that the battery was very low, the starter engaged but would not turn the engine, so I put the battery on charge for a a good few hours and now it is fully charged.

    This morning I attempted to start the car; all the lights within the instrument panel come on, fans run, radio/nav works, side, brake and headlights are fine and I'm getting / seeing 12.2 volts standing voltage when I press the re-set button on the binnacle three times. However, the starter will not engage in as much there is no mechanical noise when I move the key to the start position and none of the consumers such as heating fan, radio, and instrument warning lights etc either go dim or extinguish.

    Any ideas?
     
  2. Ted

    Ted MB Enthusiast

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    Sounds battery-ish.
    Put a voltmeter across the battery while you are cranking.
    Assuming the battery is fully charged, anything less than 9-10 volts is a strong suggestion that the battery has had it.

    That's where I would start.
     
  3. OP
    OP
    portzy

    portzy MB Enthusiast

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    Thanks Ted, it's not the battery. It was new in August this year and it's MB OEM dealer supplied, I cant get the engine to crank or even attempt to start so I cant check the voltage but I do see the 12.2 volts on the dash. I'm not getting that mechanical "click" or "tap", (relay?) when you 1st engage the start position with key, you know the sound, just before the starter motor kick in and starts to turn the engine.
     
  4. st13phil

    st13phil MB Enthusiast

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    Try moving the selector from park to neutral and see if the starter operates?
     
  5. OP
    OP
    portzy

    portzy MB Enthusiast

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    I tried that too but to no avail. After a bit of thought and noticing that neither the starter itself nor the solenoid were engaging I have researched the fuse situation and found F52 in the main, (engine compartment), fuse box to be blown. Could someone please look at the photo please to confirm my suspicions.

    I'm now wondering if there is a fault somewhere downstream with maybe the relay or solenoid, more likley the relay if I am honest so, could I ask which would be the starter relay in the second photo please.

    I think it may be the one on the far left bottom of the three, which coincidentally is right next to the F52 fuse, also, does this link look to be saying the same thing? thank you!!!!

    http://workshop-manuals.com/mercede...tarter_relay/component_information/locations/
     

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    Last edited: Dec 13, 2015
  6. zenman63

    zenman63 MB Enthusiast

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    Sounds like an EZS problem, have you tried another key?
     
  7. grober

    grober MB Master

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    Taken from elsewhere
    Start enable fuses are 31, 52 & 57. 52 usually blows & should be upgraded from 15 amp to 20 amp if your starter motor ever refuses to turn over.
    Its possible that a low battery voltage resulted in a slightly larger current draw to the starter solenoid causing the fuse to blow? First thing replace replace 52 with the same rated fuse if it blows try a 20A one again ----an ageing pre engaged starter solenoid might just be drawing too much current-- otherwise competent vehicle electrician time ----?


    http://www.justanswer.com/mercedes/...ercedes-benz-slk-r171-the-cars.html#re.v/417/
     
    Last edited: Dec 13, 2015
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  8. OP
    OP
    portzy

    portzy MB Enthusiast

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    Yes, tried both keys and cycled the lock/unlock a few times too. I'm thinking that the fuse is going to be a start point so I'll get myself a few spares tmrw, it's getting dark now, and I'm getting nervous too with all these high amperage things!
     
  9. OP
    OP
    portzy

    portzy MB Enthusiast

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    Sounds to be along the right lines, thank you. As I said, it's getting too dark now so I'll be down the shops tmrw. Just a thought though, I always thought relays were supposed to isolate the low amperage switching circuit from the higher amperage solenoid circuit:confused:

    That being the case, would or could a faulty solenoid blow the relay fuse, the relay fuse theoretically being electrically isolated from the solenoid itself.
     
  10. grober

    grober MB Master

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    At 15 amp fuse 52 will be on the main input?output from that small starter circuit relay. The purpose of the relay is essentially to switch a higher current = 15A using a very low current/voltage signal rather than that of isolation------- the ouput of the relay will energise the starter solenoid which also functions as a sort of a relay as it engages the starter but at the same time bridges the main high current contacts for the starter itself. A faulty /sticky starter solenoid would draw more current and might blow fuse 52 or your battery low voltage may well have contributed to the situation.
     
    Last edited: Dec 13, 2015
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  11. OP
    OP
    portzy

    portzy MB Enthusiast

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    So, is my understanding correct in that the small starter relay is activated via the ignition switch and that there are no fuse protection systems upsteam of the relay? i.e. it is a direct and un-fused wired connection between the ignition switch itself, in the dash, and the small starter relay adjacent to fuse 52 on the fuse board?

    Then, that being the case, the 15amp fuse 52 comes between the output of the small starter relay and the input of the starter solenoid and the fuse does in fact protect the starter relay?

    That being the case a lazy starter solenoid could be blowing fuse 52?

    Prior to me recharging the battery I am certain that all the components did engage, including the starter motor, but there was not enough poke in the battery to mechanically complete the start up.

    mmmmm, I hope its just the fuse:(
     
  12. OP
    OP
    portzy

    portzy MB Enthusiast

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    Update

    I got myself a stash of fuses this morning and replaced the blown F52 with a new one, turned the key to the start position and bingo!

    I let it run for twenty minutes or so then cycled the ignition on/off about half a dozen times and all appears to be fine and dandy now so I let it run for another thirty minutes just to let the oil and fluids get some circulation and warmth.

    The only legacy I have is that a couple off old messages have come back which are "Tyre Pressure Warning Unavailable" and "ESP Unavailable - Visit Workshop".

    In the past I have had these only for them to dissapear when the car has been run for a few miles and the battery is up to strength, MB have offered to fit a new steering angle sensor but cannot guarantee it will fix things so I will see how things go.

    Thanks for all your replies! Do you think it was just a duff fuse or a low battery that caused this or should I have an full electrical health check carried out by an auto electrician just to be on the safe side?
     
  13. Ted

    Ted MB Enthusiast

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    I would say a duff fuse, but I gave you some bum information about the battery, so don't take too much notice of what I say.
    Glad it's sorted!!
     
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  14. grober

    grober MB Master

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    I would put it down to that low battery voltage unless it goes again with the battery fully charged. Now you know where to look ---if you keep a couple of 15A spare fuses around that should guard against getting stranded in the future.
    If it goes again then time for a visit an auto electrician to get that starter solenoid current drain checked out. Every time that starter is used that fuse is thermally stressed -----if its marginally rated eventually it may succumb to the ravages of time even if the solenoid is fine.
     
    Last edited: Dec 14, 2015
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  15. OP
    OP
    portzy

    portzy MB Enthusiast

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    Hello and good morning, this problem has raised itself again:dk:

    This car is a summer car so only comes out of hibernation about this time of year and this time the fuse went, again, on a fully charged battery so I am looking to replace the starter solenoid relay this time and try that.

    So, could anyone indentify which relay it is on this diagram please, thanks!
     
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