Itermittent rear indicators fault

Discussion in 'Electronics' started by derekpayne, Jan 13, 2019.

  1. derekpayne

    derekpayne Member

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    Hi

    I have recently had a fault with the rear indicators where a message appears on the display telling me that either rear indicator has malfunctioned and the back up light is being used instead. If I turn the engine off and remove the key and wait a few moments, they revert to normal operation, I have removed the N/S light assemblt to check it, as this was the first one to start playing up, thinking it may be a bulb, but they are LED's.

    Do you think it may be a dodgy conection or is this a known fault with a work aroung solution?

    Cheers

    Derek
     
  2. Marku

    Marku Hardcore MB Enthusiast

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    When we had problems with the rear lights it turned out to be the SAM unit. Not cheap.
     
  3. zipdip

    zipdip Hardcore MB Enthusiast

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    I have the same thing with my indicators they go on then off and then on again :D:D:D
     
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    derekpayne

    derekpayne Member

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    I have stripped down the rear SAM unit, couldn't find any faults, my next theory is the light unit itself, I will have a look when I have more time.

    Has anyone else had the same problem and found the light to be at fault?

    Cheers
     
  5. alecmascot

    alecmascot Hardcore MB Enthusiast

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    Factory LED or 3rd party ?
     
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    derekpayne

    derekpayne Member

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    I believe factory as its a facelift model May 2008
     
  7. markjay

    markjay MB Club Veteran

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    Is this the CLS 320 2008 facelift?
     
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    derekpayne

    derekpayne Member

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    thats right
     
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    derekpayne

    derekpayne Member

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    I pulled the light unit out, couldnt see anything obvious unfortunately the LED indicator light unit is sealed inside the lamp, I dont want to buy a new unit until I have confirmed mine is faulty.

    Does anyone have a wiring diagram of this lamp unit? So I can test the feed as when I turn the indicators on the feed is going to the "Emergency" lamp which is the reversing light which flashes as normal, I may have to paint it amber so it looks normal, and there is no currant to the led indicators terminal, if I knew which wire fed the indicators I could wire up a temporary lamp which will enable me to test the sam properly and it would confirm the lamp unit as faulty.

    Second question, does anyone know where you can get after market rear lights cheap?

    Cheers
     
  10. Ted

    Ted MB Club Veteran

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    Don’t forget that if it is led, then it will have a different impedence to an incandescent if you want to test it.
    If the opposite side is ok it might be worth connecting to the indicator on that side (disconnecting the other side from the sam of course)
    Guessing the wires would be black/green and black/white.
     
  11. Larkone

    Larkone Hardcore MB Enthusiast

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    I had exactly this problem with my rear indicator (led) on a facelift CLS. I managed to borrow a decent garage code reader so I could look at the values and it became apparent that the LED driver would function at 12V - when the engine was off and so the battery was not charging. As soon as the engine was started and the indicators switched on it failed - as the voltage went over 13V . The only solution is whole new light unit unless you can get someone to repair surface mount components on the LED driver board.

    I managed to find a new one from one of the discount parts house ( cant remember exactly who - someone like Carparts4less) for around £170 (Lemforder i think). MB's price was around £500 if I remember right. Not had a problem since new unit was fitted 2 years ago.

    Really good system - indicator fails, whole new light unit - thanks MB, not exactly green credentials.
     
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    derekpayne

    derekpayne Member

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    Thanks Larkone, that was interesting.
    I spoke to the garage next door to where I work, and one of the partners had the same problem with a customers car, the main dealer got involved, and said that it was the light unit, they changed the light unit and it was still the same, so the dealers said it must be the SAM, they changed the SAM and the problem was cured.

    So I am still non the wiser which one it is.

    Assuming that all the LED drivers etc are inside the light unit, I should get a normal 12v feed to the plug which can be tested with a normal test light, if the test light flashes constantly it would surely mean the lamp unit is faulty, problem is when the fault appears the SAM sends the feed to the reverse light. Would a "Star" go into the system and pinpoint either unit as faulty?

    Does anyone know if it is possible to strip the lamp unit and replace the LED lights inside?
     
  13. Larkone

    Larkone Hardcore MB Enthusiast

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    It isn't possible to replace the LEDs or drivers unless you can find someone to actually replace surface mount components. I used an Autel code reader to read the voltages and that is how I determined the unit was faulty. 12V battery voltage was fine, charging voltage caused an immediate drop. If an Autel can monitor this then STAR definitely will. The other way to test is to remove the other lamp and connect that and test. If it works fine it is the original unit at fault, if the problem still shows then it is the SAM. It is easy to remove the lamp units, about 5 bolts.
     
  14. OP
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    derekpayne

    derekpayne Member

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    Thanks for that, I thought about trying the other lamp, assuming the plug is wired the same as the left and not wired the opposite way round, might try that tomorrow.

    Cheers
     
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    derekpayne

    derekpayne Member

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    Had time to delve a bit this evening, checked out the wiring on the plugs to the lights and they are wired in oposite ways so plugging in the right hand lamp to the left plug would not work, so I found which wire feeds the indicators on either side, ran a wire from the left plug (disconnected from the light) to the right plug (connected to the light) and hit the left indicator, the right lamp flashed as normal for as long as I left it, disconnected the link wire, plugged into the left lamp and the fault was there straight away. So I am 95% confident that the left lamp unit is faulty.

    Thank you everyone for your input, I will get a new lamp and report back when finished to confirm all is OK

    Cheers

    Derek
     
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    derekpayne

    derekpayne Member

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    New lamp arrived today, fitted it and all seems fine now. I wil be opening up the old lamp to see if it can be repaired.

    Cheers

    Derek
     
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