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Discussion Starter #1
Whenever I open the trunk and start to search for tools it happens. About 10-15 seconds after opening it, the light only works at about 50% efficiency. If I press the unlock button on the key fob, it works perfectly again. How can I get rid of this REALLY annoying "feature"?
Car is a b5.5, bulb is a good led.
 

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I think the CCM operates the trunk light. Possibly a switch in the latching mechanism isn't working? It appears the car knows that you've unlocked the trunk but it does not know that the trunk is open.

If you remove the carpeted cover from the inside of the trunk lid you'll have some access to the latching mechanism. Test the switches with a meter to see if they all work. A wiring diagram would probably help.
 

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The trunk light flickers slightly 10-15 seconds after opening the trunk. I suspect it's transitioning from being directly powered through the switch to being powered via the CCM. After a minute or two, the light will go out to save the battery, so certainly the CCM is involved (as the schematic confirms). In all cases, the ground is switched, not the positive.

I suggest you try an ordinary light bulb instead of the LED. It might be the electronics doing the switching in the CCM doesn't play well with the LED (think "current limiting resistor in series with the MOSFET").
 

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Leave a passenger cabin door open to prevent the transition to power saving mode and keep the LED lit at full power. I also have LEDs installed in the trunk and experience the same behavior.
 

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I added a long strip of LED lights to my trunk, but I connected it in parallel with the existing incandescent bulb. The system is presented with the same electrical loading (plus a very slight bit more current flow) as it was before the addition of the LED's. When I open the trunk, both lights come on. Every once in a while (20-30 seconds?) I do notice it flickers for brief instant but then regains full brightness. By replacing the incandescent with an LED altogether, you're drastically changing the electrical loading presented to the system.

FrescoGreen made a good suggestion. I second that you try a standard bulb first. If that makes the system operate correctly, you'll need to either add a loading resister in parallel with an LED bulb or get an LED bulb with that function built in. If that does not work, then the next thing I'd investigate is the micros witches in the trunk latching mechanism (post #2).
 

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Discussion Starter #6
Thanks for the ideas, I'll try to get to the bottom of this on the weekend. I hope I'll just need to add a resistor. I'm not sure about it but I think the old bulb didn't do this.
 

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I added a long strip of LED lights to my trunk, but I connected it in parallel with the existing incandescent bulb. The system is presented with the same electrical loading (plus a very slight bit more current flow) as it was before the addition of the LED's.
This is the correct way to do it. If the CCM had been designed for the characteristics of LED trunk lights, then all would be fine, but it wasn't.
 

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So I experimented and I found a good solution. It is not a "professional" fix, but everything is soldered an insulated properly. I installed a different LED bulb (39mm CANBUS Error Free 3 LED 5050 SMD 6418 C5W) and two other LED's (T10 White Led W5W). I'm happy with the result, it's obviously much brighter with the 3 bulbs than before. I'll take some night pictures if I don't forget.
IMG_0361.jpg IMG_0362.jpg
 

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The "CANBUS Error Free" bulb might have a bypass resistor built into it to mimic the additional current flow an incandescent bulb would draw. I'd check to see how hot that gets if left to run for an extended time.
 

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I added 3 LED's to the overhead lights in the front (near the sunroof) and haven't noticed any dimming or flickering. Huge difference :thumbup:

I will add one to the trunk soon and maybe the puddle lights.

I want to add them to the rear map lights but I can't get the housings out. I know they slide and I get one end out but not the other. Any ideas?

Thanks
 

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Discussion Starter #12
Sure, here's a picture: cp025126-hatch-trunk-dome-light-vw-jetta-mk4-wagon-gray-genuine-oe-3b9-947-113-2.jpg
Make sure you test which one is positive and negative first, this is just an illustration.
 
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