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Alarm going off

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Hi Guys,

Wonder if anyone can provide some suggestions for the issue I am having with my 2004 986 soft top Boxster RH drive, having scanned the site and trying everything I can find, am a bit stuck.

The alarm keeps going off, to the point where I had to leave work to come home due to various phone calls being received from neighbours!

So I have checked the front drain holes either side of the battery, there was no standing water and I cleared them out while I was there, no problems anyway. I have also checked for the 'tilt' sensor, as I have read this can get water logged, can't see it, so presume Porsche had moved it somewhere else by 2004!

Checked battery connections, all fine, i fitted a brand new Bosch S5 last weekend, been working fine.

Checked the rear drain holes, the passenger seat carpet was a bit wet by the firewall, that foam soaks up the water pretty good (even though the drain holes were clear - weird), I then checked to see if water got to the ECU .... It hadn't, dry as a bone. Phew!

Next I have ensured all the alarm triggers, centre cubby, roof, boot lid etc are closed down so no sensor is tripped and also that the LED sensor flashes per the manual for correct operation when locking, which it does.

Running out of ideas, so would welcome any suggestions. Otherwise, I'll have to go pay someone for a diagnostic check and chase a fault around.

All the other problems aren't as .... loud and annoying as the alarm! So can live with them for a bit longer.

Thanks very much

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Thanks for the quick response. I haven't no. I can take it to my local mechanic and get him to check, I don't have the kit myself, was attempting to try anything I could with what i have beforehand, however it might save me taking time off work to resolve though if I can get straight to the issue.

When the Alarm goes off, unlocking the car doesn't stop it, nor does switching on and driving!

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I assume that the car is equipped with an alarm siren (ROW-RHD) and it is the siren which is sounding, right? The culprit is usually the build in battery of the sirene, 2004 is fairly old for build in battery's, You can disconnect the sirene temporary to find out what it gives, keep in mind that only the horn will go off in case of theft. Put the removed siren under a big pile of old clothes or rags, until its battery is completely empty.

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Yes the siren is sounding. If its what I think it is (metal and circular) left hand side of the battery as you look at it standing in front of the car, looks like it is attached with one bolt and a electrical connector with a metal type cir-clip.

Removing this and replacing at a later date isn't going to cause any other issues other than obviously not having a siren in the mean time ...

Thanks for the help.

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I had a similar issue, after checking the codes it turned out to be the interior infrared sensor fault above the rearview center mirror. It gets activated when you lock your car and the "Red Clip" is used when the top is down or the top is up and the micro switch is activated. I ended up replacing mine and the problem was solved. . Check your codes and see if you get a "Fault 34" Passenger compartment monitoring sensor. Simple DIY. The arrows point to a Torx T-30 fastening screw that holds the sensor in place, The sensors and screws are covered by two smoke or black covered oval lenses that just pry out. careful their plastic.

The part is about $80 or so.

Turn off the sensors and see if the problem goes away.


You can turn it off the interior sensor by....

(from the Porsche manual)

Deactivating the passenger compartment monitoring system for one locking
If a person or animal remains in the car while it is locked, the passenger compartment monitoring system must be switched off.
Quickly lock car twice.
The doors are locked but can be opened from the inside:
1. Pull inner door handle once to unlock door lock.
2. Pull inner door handle again to open door.
Inform any person remaining in the car that the
alarm system will be triggered if the door is


If you click your keyfob lock button twice in succession you will get the same results. Lights will flash twice and horn will sound once.

Edited by kbrandsma
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Richard, thanks very much for the kind offer. I am very close to maidenhead infact, however a friend of a friend works for Porsche as a tech and I managed to take it 'round the back' and get it checked this morning. Only cost me a bottle of wine to say thanks!

Basically the alarm has been going off because of the 'oddments bin' according to the events log. He checked a few other things and made sure the micro switch was working correctly in the latch as well. Which it seems to be now. I asked why it would go off when driving, he wasn't sure but said if the alarm hasn't been disarmed properly before before driving off then it might still sound.

As mentioned above in an earlier post, I check the drain holes and acknowledge that there is some moisture/damp at the base of the firewall behind the passenger side (possibly hanging around from before I bought the car), he suggested I get that dry ASAP as having moisture in the vicinity of the ECU isn't a good idea, can cause condensation on the Unit and if you start getting water droplets it isn't good. Common sense I guess. So off to buy a dehumidifier and get that sorted.

Thanks for everyone's suggestions/comments.

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  • 4 months later...

I should have posted the resolution to this a long while ago! RFM was spot on, the siren's internal battery itself was the problem. Took the siren out (simple job), replaced, and all fine since.

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