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gomi_otaku
gomi_otaku, VW Technician
Category: VW
Satisfied Customers: 3378
Experience:  VW FastTrack '00-'01, VW Academy Chicago and Seattle '00-present, VW Certified
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I have a 2008 VW Beetle. The rear latch won't open the

Customer Question

I have a 2008 VW Beetle. The rear latch won't open the trunk. The plug going to the module actuator (solenoid) has 12 volts constant. Is that the problem? The actuator does respond to 12 volts input.
Submitted: 1 year ago.
Category: VW
Customer: replied 1 year ago.
I tested the system with the plug to the actuator removed. The remote key button lit the security system lights and the door trunk switch sent 12 volts to the actuator. Still, why does the actuator plug have 12 volts all the time?
Expert:  gomi_otaku replied 1 year ago.

It is ground side activated.

The problem, if you remove the trim panel and look at the backside of the system, is the linkage between the solenoid actuator and the latch itself.

Customer: replied 1 year ago.
That does not make sense. The actuator is a separate unit from the latch mechanism. The actuator unit is a plastic material.
Expert:  gomi_otaku replied 1 year ago.

I'm sorry if that was unclear- the way the actuator activates the latch, there are a lot of internal failures. We just replace the whole latch assembly.

Customer: replied 1 year ago.
The linkage between the actuator and the latch is a mechanical lever. The actuator does not respond to the input switch or remote control. The problem is electrical. The two wires coming into the actuator activates the actuator with 12 v. The wires have a 12 volt constant charge on them. I don't think that is correct. When I connect the wires to the actuator, the actuator freezes and won't respond with the switches.
Customer: replied 1 year ago.
Are you familiar with the 2008 VW Beetle convertible trunk assembly?
Customer: replied 1 year ago.
The actuator and the latch mechanism are separate units.
Expert:  gomi_otaku replied 1 year ago.

you never said it was a CONVERTIBLE!! Have you tried disconnecting the trunk release lever on the driver door? I have had those fail a lot- and since the signal goes THROUGH the comfort module, the system learns to ignore the constant input.

Also, you may have 12v, but the amperage may not be enough to trigger the actuator.

Customer: replied 1 year ago.
Can the problem be somewhere else other than the actuator? Otherwise, why does the positive 12 volts stay in the line?
Customer: replied 1 year ago.
I did a check on the driver door switch for the trunk. I connected a meter to the plug that goes into the actuator and measured the voltage when I turned the door switch on. It read 12 volts. When I turned the switch off the 12 volts went to zero.
Customer: replied 1 year ago.
What and where is the comfort module? Can that be the problem? How can I check that?
Expert:  gomi_otaku replied 1 year ago.

Try disconnecting your battery, and touching and holding the two CABLES together without touching the battery at all- for about a minute. This will reset the module. SOmetimes they get stuck (like a computer running Windows!)

Customer: replied 1 year ago.
What amperage is the constant 12 volts in the system and how much amperage does the actuator need to trigger? Could the problem be a faulty actuator? The actuator does work when I attach a 12 volt line from a battery.
Customer: replied 1 year ago.
I did run a check on everything in the car. The only thing not working was the trunk release. If the comfort module was stuck wouldn't other items not work also? Also, is there a fuse for the trunk actuator? I could not find it in the manual.
Customer: replied 1 year ago.
Also, If I disconnect the battery, as you recommend, and it does not work, can we talk again without an extra charge?
Customer: replied 1 year ago.
I won't be able to try that advise until tomorrow. Do you work the weekend?
Expert:  gomi_otaku replied 1 year ago.

I don't know what the amperage load would be for the actuator (VW doesn't publish specs like this) but I know I have had other circuits that have acted like this (A/C compressor for one) where voltage was "leaking" into the circuit. Probably because everything is run through microprocessors now, not solid state circuitry.

And yes, you can come back anytime. I don't get paid from your deposit with the site until you "accept" my answer. If you are gone for a few days the site might send you reminders, just know they are not specifically from me but from the site.

Customer: replied 1 year ago.
Ok. I will try disconnecting the battery cables and shorting them (without touching the battery) for 1 minute to see if that will reset the module. Thank you.
Expert:  gomi_otaku replied 1 year ago.

ok, just let me know what you find.

Customer: replied 1 year ago.
I tried disconnecting the battery terminals and connecting them for a minute. Then I connected them. That did not effect the problem. Another thing that might help you to help me. I noticed a relay under the dash clicking when I lifted the door switch for the trunk. It is located on a board with a group of other relays. The click was immediate when I lifted the switch, then it clicked (released) again after about 2 seconds. To me, it means the door switch and the remote key switch are working. The relay sounds like it is also working. And when I measure the current at the plug going into the actuator it changes current. The amount of current is confusing me. It changes from a plus 12 volts to a negative 12 voltage. I understand your comment about digital versus analog circuits. All of this sounds like the actuator may have a disfunction. However, when I bench tested it with a 12 volt battery it functioned properly. My logic points to the polarity and/or amperage going to the actuator. Could the relay under the dash cause a reversed polarity going to the actuator? If it were reversed with a constant negative voltage then reversed to a positive 12 volts when switched, it would activate the actuator. The thought of turning the plug into the actuator occurred to me. The plug is keyed to insert in only one way. I could try the theory with wire and clips but that is not the answer. It would tell us if the amperage was enough to trigger the actuator.
Customer: replied 1 year ago.
OK. I had to try reversing the polarity of the wires going into the actuator and then I pressed the remote switch. The actuator worked slightly like it did not have enough voltage/amps to fully engage the actuator. I measured the voltage again going into the actuator plug. It measured (minus) -11.45 volts. When I pressed the remote switch the relays under the dash activate, the rear lights go on and the plug voltage is (plus) +.38 volts. Then I connect the plug into the actuator and I press the remote switch... nothing, no rear lights, no relay under the dash activity. All of this seems to point at the relay under the dash. Exactly, which relay is it? Is the relay unplug-able? Can I take it out and bench test it?
Expert:  gomi_otaku replied 1 year ago.

the "relay" you hear clicking is likely the comfort control module- which is located on a bracket just to the left side of the steering column. If you remove the left end of the dash (where the door over the fuse panel is) and also remove the underdash cover, you will be able to see it, it is a black box with two large connectors to it. (You can view it just through the dash endcap, but to be able to remove it, I like to view through the endcap area and use tools under the dash)

Customer: replied 1 year ago.
Ok. I have three questions from your response. Based upon the symptoms, has the black relay box caused these problems before? Does the black relay box easily pull out of a receptacle on the printed circuit board? Is there a bench test that I can check it?
Expert:  gomi_otaku replied 1 year ago.

The comfort module is not a relay- it is a whole module in itself, that controls all the functions of the windows, door locks, and relays other messages between the door modules like for switch illumination. There's no real way to test any individual circuit at the pins. The module is removed by removing a pair of phillips screws that mount the backing plate to a bracket near the steering column, and disconnecting the two connectors.

And this module has been known to do all kinds of strange things if a circuit goes bad- only allowing one door to unlock with the remote, for example, when they are all supposed to unlock, is the most common issue. It sounds like yours is bleeding voltage into that circuit, but then when that circuit is activated (as evidenced by the fact that it flashes the blinkers) the amount of amperage it sends to the latch is not enough to unlock it.

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