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Discussion Starter #1 (Edited)
05BS 987

I didn't find a thread that answered this question so I'm hoping someone can help me.

I had some LEDs go out on my headlight switch, so after ignoring it for a year I decided to install a new headlight switch. It was working just fine, and still is, for a few days. Today I re-installed the old one to see which lights were out, then re-installed the new one. After I did that, all the lights are still working perfectly. However, when I engaged the ignition to check that the headlights would come on, I heard a buzzing sound from the frunk/front bumper. It's somewhat loud.

I finally determine where it's coming from, some sort of sensor perhaps located just above the front bumper. I remove the black trim and can see and touch (feel the vibration) this part. The only way to get it to stop vibrating is to DISCONNECT THE BATTERY. Reconnecting the battery, the sound returns as soon as I engage the ignition. Again, I have to disconnect the battery to get it to stop.

At first I was getting a System Fault code plus a PSM Failure code. I read that driving around might reset PSM, and it did reset the PSM after a mile or so. But the buzzing from that part is constant until I disconnect the battery. I still get a System Fault code.

I can't find a parts diagram that shows me what I want. Here's a photo taken identifying the part. It has this little cable that extends about 5 or 6 inches to the right (passenger to drivers side) if you're facing the front of the car. This photo was taken from above.

Anyone experienced similar? What is this part?
 

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Discussion Starter #3
Looks like it's the "Actuator emergency operation" p/n 996-624-119-01. Is that the actuator that's activated when you jump-start the car via the fuse panel terminal?
Yeah, that's what it is. I'd have to take the bumper off just to unplug the damn thing. The part is only $80. I need an oil change so I'll just let my independent mechanic deal with it all. Hopefully the front control unit ($400) isn't part of the problem.
 

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I love reading about this stuff; someday one of these problems will crop up in my car.
 

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Discussion Starter #7
Are you still using the old light switch, or did you put the new one back in? Try putting the new one back in if you haven't already.
Yes, I've tried both switches. Even without either switch in place, the problem persists.
 

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I don't think the actuator itself is the problem. Assuming this is designed to open the frunk via the +terminal in the fuse panel if/when the battery is dead (I can't find any confirmation online), it should not be getting power at all. But if it's buzzing, that means it's getting power. It doesn't appear to be getting enough power to actually open the frunk, though, just buzz, which it's not getting 12V. I would look for an electrical fault/failure elsewhere- bad ground, bad relay, etc. Working with the light switch may have disturbed some wires at the fuse box- see if something got knocked loose, or if there's a blown fuse. Is anything else not working? On my 986S, the fuse for the emergency relay to power the locks (C3) was the same fuse for some of the sensors PSM uses (no clue why...) which may be a clue.

In the meantime, you may be able to just unplug it. Would complicate matters if you ever let the battery go dead, but would at least stop the buzzing.

Found another thread here about it; again, no resolution:
http://www.planet-9.com/987-cayman-boxster-problems-complaints/55984-problem-mystery-part.html
 

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Discussion Starter #9 (Edited)
I don't think the actuator itself is the problem. Assuming this is designed to open the frunk via the +terminal in the fuse panel if/when the battery is dead (I can't find any confirmation online), it should not be getting power at all. But if it's buzzing, that means it's getting power. It doesn't appear to be getting enough power to actually open the frunk, though, just buzz, which it's not getting 12V. I would look for an electrical fault/failure elsewhere- bad ground, bad relay, etc. Working with the light switch may have disturbed some wires at the fuse box- see if something got knocked loose, or if there's a blown fuse. Is anything else not working? On my 986S, the fuse for the emergency relay to power the locks (C3) was the same fuse for some of the sensors PSM uses (no clue why...) which may be a clue.

In the meantime, you may be able to just unplug it. Would complicate matters if you ever let the battery go dead, but would at least stop the buzzing.

Found another thread here about it; again, no resolution:
http://www.planet-9.com/987-cayman-boxster-problems-complaints/55984-problem-mystery-part.html
I've been having similar thoughts as to why it's getting power at all. I thought maybe at ignition-on the control unit does a check (similar to CANbus checking a light bulb) and that triggers the motor into this 'stuck on' state. Nothing else electrical seems to be malfunctioning. I even tested the emergency frunk opening procedure with jumper cables. All lighting is working. Unplugging the actuator requires removing the front bumper which I can do but am not excited about (because I'd have to put it back on just to drive it to get it serviced, where I'll be probably paying someone to do it again anyway).

I would be shocked if I put any stress on the headlight switch cable enough to cause a problem under the dash, but I suppose anything is possible. I might poke around a bit more.

I appreciate your time and ideas - thanks!

EDIT: BTW, aside from the emergency actuator, the frunk opens normally with the remote. The emergency actuator is not what opens the frunk when you use the jumper cables. At least on my 987, it is only used via the handle inside the frunk. The actuator merely releases the frunk 'catch', which from the outside of the car, we all do by hand after releasing the frunk lock mechanism. Disconnecting the cable at the inside handle does nothing to fix the problem either. It must only provide a signal to the control unit to activate the actuator. I hope the control unit ($400) isn't bad.
 

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I'm just curious- I'm an engineer and enjoy troubleshooting weird problems like this is fun; moreso when it's not happening to me, lol.

In the absence of any information, I suspect this part is a redundant electric frunk release to permit access if the primary actuator fails or if the battery fails. It carries a 996 part number but I looked through my Bently 986 manual with no luck. The 986 does not have this, but does have an emergency relay that provides power to the alarm control unit. It's normally powered by the battery, but if +12V is placed on the emergency terminal in the fuse panel, the SPDT relay switches the alarm control unit power source from the battery to the +12V emergency terminal so that a dead battery (or fault) won't interfere with the ability to power the control unit. It also shunts +12V power directly to the horn. I *suspect* the 987 also has this emergency actuator in parallel so that when the relay is actuated, it receives power, pulling the frunk release handle. Without a wiring diagram, I can't tell though, but it would make sense: it's what I'd do.

On the 986, the negative side of the relay is connected to ground point CP1GP3, which I think is right by the fuse box. If 987 is similar and there was a fault putting a partial voltage on this terminal, it *might* be putting a slight negative voltage on the emergency actuator and create the buzzing. An open ground on a circuit in parallel (like the horn or alarm) might be pushing current to ground through the secondary terminals on the relay, which could also cause this.

Next troubleshooting step may be to use a voltmeter and see if there is any voltage on the emergency +12V emergency terminal or GP3 ground points.
 

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Discussion Starter #11
Next troubleshooting step may be to use a voltmeter and see if there is any voltage on the emergency +12V emergency terminal or GP3 ground points.
OK, you lost me at C3PO :) Er, GP3. I looked at this diagram (987.1 Wiring Diagrams - Downloads - Planet-9) and I think I want ground point 7? I took a voltage meter and confirmed 12.25v at the battery. Then I tested the emergency terminal in the fuse box (+) to the driver's seat rails (-) (bolted to the floor of course) at 0.00v and the emergency terminal in the fuse box (+) to the door latch (-) (where the manual instructs to emergency open the frunk) at 0.00v. I did these with and without the ignition on. Every time, like before, the emergency activator motor starts buzzing once I turn the ignition on, and every time I have to disconnect the battery to get it to stop. [When I say 'turn the ignition on' that doesn't mean 'start the car' -- starting the car has produced no different results. Driving the car does reset the PSM failure, but that seems to be a normal thing after disconnecting the battery.]
 

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guys,

the 987 bumper is not very far from the 981 bumpers.. I have taken out both.. i have a recent blog on how to take out the 981 bumper.. but its really close...

lemon
 

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Discussion Starter #14
guys,

the 987 bumper is not very far from the 981 bumpers.. I have taken out both.. i have a recent blog on how to take out the 981 bumper.. but its really close...

lemon
Yeah, it's not THAT difficult. I've done the rear bumper. I just figure this one isn't worth my time. I'm sure unplugging the actuator will make the problem go away, but once I get it off I'll have to put it back. For 2 hours shop labor, I'll give my local shop some business.
 

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Looking over that wiring diagram, another possible culprit is a failed-closed "emergency luggage compartment open switch" which I can't locate in the catalog parts diagrams. It has yel/red and brown wires to it, if that helps you find it. You may be able to trace the wire from the front end control unit (right side of the frunk).

And this may sound dumb, but check to make sure the normal luggage compartment button by the driver's seat isn't sticking.
 

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Discussion Starter #16
Looking over that wiring diagram, another possible culprit is a failed-closed "emergency luggage compartment open switch" which I can't locate in the catalog parts diagrams. It has yel/red and brown wires to it, if that helps you find it. You may be able to trace the wire from the front end control unit (right side of the frunk).

And this may sound dumb, but check to make sure the normal luggage compartment button by the driver's seat isn't sticking.
Unlocking the frunk via the key remote or the compartment button does not trigger the problem. The only two things that cause the actuator motor to buzz non-stop are 1. turning on the ignition and 2. pulling the emergency lever inside the frunk. The two wires that run to the emergency lever are red/yellow and brown. If I disconnect the wires from the lever, turning on the ignition still triggers the motor buzzing. So I suspect the switch for the actuator is at or inside the unit itself?
 

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Discussion Starter #17
Just to update, this is now fixed.

My mechanic found dozens of fault codes, had to clear them twice, but eventually got the front control unit to behave again. I didn't need parts but it was a couple hours of trial-and-error labor with the Durametric/ignition on-off/battery disconnect.
 

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Discussion Starter #18
And it's back. Didn't do anything to trigger it this time, just started the car. So I guess I'll go back to my mechanic and see if we can't reset it. At this point I'm wondering if the control unit or actuator need replacing to permanently solve the problem.
 

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Discussion Starter #19
I ended up replacing the frunk emergency actuator a few weeks ago and so far it hasn't wigged out again.
 
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