Mystery frunk noise?

I just replaced the under-seat ECU * in my 2005 Boxster S (the one that controls windows, spoiler, convertible top, etc.) following a heavy rain that soaked the unit. Now everything works again as it should, except that I now hear a constant whirring noise from the front trunk, behind the bumper. I assume it’s a radiator cooling fan, but can’t guarantee that. Noise is constant regardless of whether ignition on or off. Only disconnecting the battery stops it. *I think “rear control unit/module” is the appropriate term. It’s the one under the left seat that is susceptible to flooding. What’s the fix? Is this a harmless and routine side effect of replacing the rear control module under the left seat, or of having the battery disconnected for long periods? Or is something broken? Update: Problem solved. It wasn't a cooling fan; it was the electrically actuated hood release that only gets used when you pull the emergency handle inside the front trunk. Either the actuator or its controller got damaged, probably when the RCU got wet.

It's not normal. If you have a Porsche specific diagnostics tool you could look at the fan controller and see what it thinks it's doing, and perhaps why. I might be the fan controller was damaged when the control module was soaked. If there are any stored codes that might be a clue, and you might use the tool to reset the codes, or even redo the "handover" procedure which seems to be needed when larger electrical issues happen on this series of 987's. The fan running continuously isn't normal.

BTW - when you solve the mystery, please come back and post how. And when you have a chance, please visit New Member Introductions and tell us about you and your 987. Photos are always welcomed!

Thanks, will do. In the interim, is there a fuse or a relay I can pull to temporarily disable the fan(s)? I've disconnected the battery for now to prevent the fan from draining it, but I obviously can't drive the car that way. I've looked at a 987 Boxster/Cayman fuse map and nothing obviously jumps out at me.

Update: It's not the fan! I mistakenly identified the noise up front as radiator fan(s), but that's not the source. I checked by sticking my hand into the fan blades: they turn easily whether the car is on or off, so they don't seem stuck. And the fans shouldn't be coming on when the car is stone cold, anyway. The noise is coming from slightly off-center to the right (passenger side in US). This quick video may help someone identify the sound. Could it be the headlight washer pump? Headlight washers don't seem to work at the moment even though the reservoir is full of water. (Windshield washers do work.) Or maybe it's the car horn bleating for help? Something to do with the car alarm? Or some other electro-mechanical device that lives behind the bumper?

headlight washer pump is attached to the washer reservoir behind the front left wheel.

You could systematically pull and reinsert all fuses one at a time until the sound stops. That might at least narrow the possibilities. Using that little yellow fuse puller tool, it should only take few minutes. Edit: Wow, I just listened to your vid. That is a loud noise. Buy a stethoscope for a few bucks ( Harbor Freight ) and localize it.

Just a guess, but is the fuel pump around that area?

It's not too far away. I believe it's an immersion pump in the tank, which is just ahead of the firewall of the frunk. One thing I thought of it could be - and it does run sometimes with the ignition off.. @RoadHazard asked in another thread what the black plastic box with clips is - the one located in the bulkhead that covers the fuel tank. I 'splained that was an emission monitor device. Well... that device has a pump in it that pulls a small vacuum on the fuel system to see if there are any leaks. I believe that the pump can run ignition on or ignition off. That's the only thing I can think of in that area that might behave in the manner RoadHazard described. So that's my guess (pending his getting a stethoscope and tracking it down.)

just taking a wild guess - could it be the frunk release mechanism? if you could take off the bumper, it might help your diagnosis and check the horns, fans. Yes the horns are a known issue.

Could be. It's in the right area, but the frunk release still works fine. I've also pulled all the fuses I can find in the footwell and it doesn't stop.

Welp, just finished trying that and the noise didn't stop. I pulled every fuse one by one in the A, B, C, D, and E rows that I could find in the footwell fuse box. Disconnected and reconnected the battery before/after each fuse. No change to behavior with any of them. I'm surprised. I figured whatever is making that noise must pass through that fuse box, but apparently not.

FOUND IT! It's the front trunk release mechanism. Or rather, it's one of the front trunk release mechanisms. But now I'm more confused than ever. The noisy gizmo appears to be a plunger that pulls a short cable laterally toward the right side of the car, unlatching the frunk. It's connected by two wires, red and orange, accessible from underneath. Reaching up through the center radiator opening and disconnecting these two wires stops the noise. Hurray! Oddly, the normal frunk release switch (the small switch by the driver's side door sill) still works. Huh? And I'm guessing the emergency cable release still works, too. How many release mechanisms does this thing have? And why didn't removing the fuses kill it? Is this circuit not fused, and if not, why not? View from above front bumper showing faulty release mechanism. (Forward is down.) View from below the front bumper looking upwards at faulty mechanism and its electrical connections.

I don't think those are the hood release wires. First clue is the release switch still works! I checked the 987.1 wiring diagram and there are only 2 wires to the release and they are brown (ground) and brown&black (+12v). These come from the front-end control unit. I found a circuit in that vicinity with a RED and BRN/ORG wire pair - something oddly called "Drive Hooks". No idea what that is or what disconnecting it will affect. Might have something to do with HomeLink (whose controller is just below in your top photo. Might also have something to do with your center fan but that's just a wild guess. BTW, did you test the Frunk Open from both the driver door switch and the key fob? Does Homelink work? There are other fuses in front and rear compartments. They are hidden behind carpet or trim.

I should clarify. When you pop the hood normally, it opens only partway, at which point you have to reach your hand under the hood and manually release the safety catch (red lever). This mechanism seems to automate that process, pulling the safety catch under electrical control. I can’t imagine why you’d want such a feature, or how it’s considered safe, but there it is. Its sole purpose seems to be to pull the red lever for you.

I've never heard of that - and there's no such "feature" on my 987.2. However I just popped-off the black trim to look and mine looks just like what you've circled in red. I believe it's actuated by the red lever to release the final latch. I don't believe it is electrically actuated. I think what you disabled is some switch or sensor either part of an alarm, immobilizer, or safety alert. For example, the horn is supposed to beep if you attempt to lock the car with the lid unlatched. There is at least one micro-switch in there somewhere. BTW, there is a separate small alarm horn, but I think it is up near the battery.

I have to agree with your supposition on what it does.. now, as to WHY it does it? I can only try turning on my German side for engineering.. ya? If ve have a fire in the fuel tank/fuel system, flames might be coming out of the frunk in the gap between the lid and the front bumper ya? If so - you don't want to burn fingers? Sooooo.... in the vent of a fire ve automatically release the secondary locking mechanism for the front lid und you can spritzer with the fire extinguisher under the front of the passenger's seat. Make sense? Not a lot - but I can't think of any other possible reason for it. As to why it's making noise - well - I think you have to connect to the front module and see what it thinks is going on..

On second thought, I think it is an active component after all, not a sensor. The schematic shows it as a solenoid, and it’s labeled “drive” just like the tailgate and front hood drive solenoids. It’s also a pretty elaborate plunger and cable arrangement for just a dumb on/off switch. It really a looks like it’s designed to pull the safety latch back… for whatever reason. As for the fuse, I’m guessing it’s one of the ones buried in the side of the frunk, which I never tried pulling.

So I'm assuming you pulled the BRN/ORG and RED connection to the component labeled "DRIVE HOOKS" and which goes back to the Front End Control Unit to the "HOOKS UNLOCK" connectors. This is similar to the "LUGGAGE COMPARTMENT HOOD DRIVE" component with one big difference - it only has one wire to the Front End Control Unit (BRN/BLK) the other wire is just a ground. Both components appear to be solenoids. The big questions are - what do they control and why? At first the DRIVE HOOKS seems to be redundant. And since you unplugged it that seems to confirm that is isn't necessary for normal operation. Still, I suspect they are triggered differently. And the difference in grounding might be a clue. You once stated you thought the noisy solenoid was to release the second (safety) latch. I'm not sure - can't tell just by looking from above. But I am curious about something else in that diagram - the "EMERGENCY LUGGAGE COMPARTMENT OPEN SWITCH". I don't recall ever hearing of this. It goes back to the Front End Control Unit, so it triggers something there. Maybe this solenoid? And if that switch or the YEL/RED wire got shorted - it could trigger the "HOOKS UNLOCK" solenoid continuously and turn it into your noise maker. Or since it is for EMERGENCY, the Front End Control Unit might have logic to trigger it if the circuit is open. In fact, this might have some purpose to unlock in case of a collision. Anyway - If you have all that trim and carpet removed, I'd take a look at that switch. Follow the YEL/RED wire. Once you find the switch, make sure it is grounded to GP1.

So, I had a look at the 574-page Boxster parts list, and the mystery gizmo appears in Illustration 803-000 as item #17, described as "throttle control element Emergency operation." Ooookay... "Throttle" seems like an odd description here, but "emergency" is pretty clear. Methinks it's some rarely used safety measure. At any rate, my next job is to figure out which part(s) to replace. The noisy solenoid is bound to be cheaper than the electronic unit that controls it, but the latter seems more likely to have been damaged in the water-intrusion incident that started all this.

A-ha! NOW I get it! This is all part of the anti-kidnapping safety release in case someone gets trapped inside the front trunk. The "emergency luggage compartment open switch" in the schematic is actually the big glow-in-the-dark handle inside the frunk. It activates item #16 to pop the hood. But, since the hood has a red safety latch that's only reachable from the outside, it must also activate that, which is what item #17 does. So, pulling the handle unlocks both hood releases at the same time. Presumably it also cuts the throttle so that the kidnapper/getaway driver is forced to stop the car before the hood flips up in his face (hence the "throttle control element" description in the parts catalog). Clever, those Germans. Me, not so much.

I had another idea on why the alternate/extra solenoid. Maybe it is used for the emergency unlock method when the battery is dead of defective. It would make sense to have a simple and separate system that is isolated from the main battery . See Emergency Frunk Unlock. The issue with that theory is why would it be getting power in your car without jumpers attached? Did you mess around with anything near the fuse box or any wiring in the frunk before you had this issue? Or possibly water damaged/shorted something.

So the emergency switch might be faulty causing constant power to the actuator. BTW I like your explanation better than the dead battery theory I just posted.

I definitely did have water under the driver's seat that fried the rear control unit and caused all sorts of crazy behavior until I replaced it. Then everything was back to normal except for this odd buzzing sound. My guess is that the waterlogged RCU sent all sorts of bogus commands to the front control unit, which then did bad things to this actuator. The actuator itself didn't get wet.