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Driver rear tail light dimly lit when car is off

Discussion in 'Roadster' started by Rik, Sep 9, 2015.

  1. Rik

    Rik Member

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    Location:
    Northern VA
    I've found that my 2.0 driver side rear tail light remains dimly lit (no other lights on and does not matter if light switch is on or off) after the car is off. it will remain on until it finally decides to turn off... this occurs randomly and can do this for days. No real impact on battery.

    Here's a photo of what it looks like. Unless it's completely dark, I typically have to cup the light with my hands to see if it is the reason my rear fan is running.

    SC has looked at this a couple of times over the past several months. Last visit to Tysons was a 2 week stay where their best guess was a faulty tail light. They said they could not reproduce and that supposedly there was no power draw the entire time it was with them. I'm at a loss and concerned more about what else may be awry and the longer term impact on power draw.

    Anyone seen anything like this?
    Toughpad - 1.jpg
     
  2. spaceballs

    spaceballs Member

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    Sammamish
    My guess is a mosfet in the switchpack is not fully turning off from time to time.
     
  3. Chickenlittle

    Chickenlittle Active Member

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    Funny have noted the same in my 2.5 roadster. Same light. Wasn't sure it was really on, so faint. Just went through annual service and inspection. I had forgotten to mention it. If you find out issue let me know please
     
  4. Rik

    Rik Member

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    That's greek to me but I'll pass along to the SC. Thanks!

    - - - Updated - - -

    Which SC did you go to for your annual service? I will want to raise the point that you are experiencing this too. So far, I cannot relate when it happens to charging, temperature, charge settings, cool downs, charge port open or closed, last door opened... nothing.
     
  5. Chickenlittle

    Chickenlittle Active Member

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    Tyron's corner/ tyco rd. looked last night, not on anymore but it was intermittent in past. Light not bright at so subtle I at first thought it was reflected but not
     
  6. wk057

    wk057 Senior Tinkerer

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    Almost definitely a fet partially stuck partly closed. (A mosfet is basically a digital relay/switch with no moving parts). Is that light LED or an incandescent of some kind (I'm not familiar enough with the roadster)? If it is the latter then it wouldn't surprise me if the mosfet is leaking a little after years in service since it would be handling a slightly inductive load. The flyback diode may have also weakened over time and accelerated the wear on the mosfet, or may not exist entirely depending on the design.

    Basically it is probably more trouble to fix than it's worth. It's literally a $0.25 part on a circuit board that is likely inside a larger module that is way more expensive. If the amount of current leaking is negligible, I'd probably leave it alone. If it gets brighter over time... well, then you're going to have to look into a repair probably.
     
  7. bigbill

    bigbill Member

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    That's a good possibility. Another is that some water made it onto a PC board. This can cause oxidation, which can create an intermittent path with resistance across some of the traces.
    Another possibility is a strand of wire has broken off of a connector at the crimp and is sometimes contacting the connector next to it.
     
  8. mookhead

    mookhead Member

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    Happened to me too. Switchpack switchout fixed it.
     
  9. Timothy

    Timothy Driving on Sunshine

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    Mine did this too for months--then healed itself before I had the car serviced 2 years ago! Hasn't happened since.
     
  10. jimmyz80

    jimmyz80 Member

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    The service records for my roadster indicate that it had this problem early in its life. I believe the "fix" was replacing the tail light. From reading this thread, it seems to be more common that I would have expected.
     
  11. Rik

    Rik Member

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    so the fix thus far was SC replacing PEM and tail light.
     
  12. mookhead

    mookhead Member

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    I should have followed up on my experience...

    After replacing the switchpack, the problem re-occurred (or never went away, it's hard to see), so days before my extended warrantee expired, I took it back to the Fremont SC, whereupon:

    1. 7 days into it, "we can't reproduce". I drove over, pointed at the problem, they went "ohhh", got back to work.
    2. 2 days later, they call me to tell me they need replace my PEM
    3. 24 days later (!), they install new PEM
    4. 2 days after that, they call me to tell me it wasnt the PEM after all, and that they installed a new tail light and that fixed it.

    Sheer comedy.
     
  13. ElectricLove

    ElectricLove Member

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    Very efficient servicing indeed...
     

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