Weird Trunk lock Problem
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    1. #1

      Weird Trunk lock Problem

      I could not find anything on the internet about this problem. My trunk in my 2005 s40 keeps on locking and unlocking randomly... It happens while i'm driving and it happens even when the car is off and parked. Also, every time I turn the car off, the trunk pops up.
      My question is, is this a wiring problem, or could I just replace the locking mechanism and fix it? Has anyone else had this problem?

      I unplugged the pigtail from the trunk lock and I stuck my multimeter in what I assume is the power and ground and it read about 1.25V and every once in a while it would jump up to 11 or 12 volts... the car was off with the key out when I did this. Before I unplugged the mechanism, it was going crazy locking and unlocking so I assume that every time the voltage jumped up to 12 it triggered the lock.
      so based on that, I assume that this is a wiring problem and my lock is good .
      Does anyone have any ideas on what else I could test to try and figure this out? Any help is appreciated.

      Hope this makes sense.

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    3. #2
      Member pczeilon's Avatar
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      2007 V70 5 Speed
      2005 S40 2.4i 5 Speed

      1995 855 5 Speed SOLD

    4. #3
      I bought a replacement harness and it still did not fix it. In fact now the trunk will not open when I press the button when it did before. Can someone help me out?

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    6. #4
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      I'm not sure that the trunk should open when you press the trunk button - it should just unlock. Check and see.
      2005 V50 T5 AWD M66

    7. #5
      Quote Originally Posted by tatertoph View Post
      I bought a replacement harness and it still did not fix it. In fact now the trunk will not open when I press the button when it did before. Can someone help me out?
      My problem was the switch and not the harness (which I replaced first). Good news is that the switch is only about $15 and not hard to replace.


      Sent from my iPhone using Tapatalk

    8. #6
      If your glove box is locked, the trunk wont open even if its unlocked... FYI

      (Valet mode)

    9. #7
      Quote Originally Posted by mercdude View Post
      I'm not sure that the trunk should open when you press the trunk button - it should just unlock. Check and see.
      I meant that it will not unlock when I press the button above the license plate.

    10. #8
      Quote Originally Posted by sheinb View Post
      My problem was the switch and not the harness (which I replaced first). Good news is that the switch is only about $15 and not hard to replace.


      Sent from my iPhone using Tapatalk
      Thanks I'll try that next. What switch are you talking about?

    11. #9
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      Quote Originally Posted by tatertoph View Post
      I meant that it will not unlock when I press the button above the license plate.
      The switch that is a part of the trunk - it's either the harness has a problem or the switch itself. You could check the physical lock also and make sure it hasn't come apart internally. Does the switch try to unlock when you hit the button? or not?
      2005 V50 T5 AWD M66

    12. #10
      Quote Originally Posted by mercdude View Post
      The switch that is a part of the trunk - it's either the harness has a problem or the switch itself. You could check the physical lock also and make sure it hasn't come apart internally. Does the switch try to unlock when you hit the button? or not?
      When I press the switch nothing happens, and the physical lock seems to be in good condition. The weird thing is that every time i turn the key to off, the trunk unlocks.

    13. #11
      Do you think resetting the computer would work?

    14. #12
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      Quote Originally Posted by tatertoph View Post
      Do you think resetting the computer would work?
      It's possible. When I had a break in my harness I would frequently get the 'trunk open' message. After a while it eventually went off (and I still couldn't open the trunk).

      So I hooked VIDA up and saw there was a code for "trunk switch signal too high" (or something along those lines). I took that to mean that the ECU saw the switch was being triggered too often (broken wires touching), so it disabled power to that circuit. After clearing the code, I was able to open the trunk.

      Disconnecting the battery for ~10min should do the same thing.

      If you haven't tried a new switch yet, I would go that route- they're only ~25 bucks.
      2007 S40 T5 AWD

    15. #13
      Hello all.
      This trunk issue is a common one for these cars.
      It happens to myself for 2 times, and every time i had to repair the broken wires from the harness. Also i have changed the switch part every time.
      It operated right away without any reset with Vida.


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    16. #14
      Junior Member msmith's Avatar
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      It is a common issue. Happened twice on my S40. First time I replaced harness and switch. Second time (recently) we had the wires pulled and repaired.
      2012 S60 T6 AWD | Black/Beechwood | Premium/Climate Package | BLIS | Sunroof | Active Bending Bi-Xenon (mine)
      2006 S40 2.4i M56 | Barents Blue/T-Tec | Sports Package | Sunroof | OEM Tail | 3M Clearbra | Fogs | Parrot Mki9200 | K&N Air filter (sold to son)

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