Alarm Not Working Correctly

[PaulR]

Today I came back to my car to find the alarm siren sounding and the hazard lights flashing. I now notice that the hazards do not flash as they should when the doors are locked (alarm activated). I have checked that all four doors and the rear door all operate the interior lights correctly, when being opened and closed. I have released the bonnet before locking the car, waited for the alarm to activate (according to the LED's) and then opened the bonnet. This does not trigger the alarm as I believe it should, so am I to suspect the bonnet sensor may be faulty, as suggested elsewhere on this site? If so, where is it, behind the grill, or in the lid, and is it a reasonable diy job to check and if necessary, replace?

As ever, appreciate your help.

...Paul.

[Jarv]

Hi Paul,

This happened to me recently, couldn't work out what was setting the alarm off. Did a VAGCom scan and it was coming up with alarm triggered by bonnet catch, so I disconnected it and it's all OK (apart from the fact that the alarm doesn't go off if the bonnet is opened). The switch is in the bonnet catch on the front slam panel, you can just about get in there with a flat bladed screwdriver to slide the plug apart. If you have VAGCom, give it a scan and see what DTC's come up.

If it is a faulty switch you have, I have no idea how to replace it, but I'm guessing it's not that difficult.

Hope this helps

Mike

[PaulR]

Thanks Mike. I haven't got VAG Com, but have had a look. I can see the switch, and the wires, but not how it is activated. I may well try some WD40 next, before disconnecting it. Oh, and have a proper look in daylight.

...Paul.

[Jarv]

Nice one, if it is the switch that's faulty and you do end up changing it, keep us updated as to how easy it is as I really should do mine.

[PaulR]

WD40 seems to be the answer. I have got the single flash back when the system arms, and it has been active now for about 30 mins without a false alarm. I really shouldn't be writing this until tomorrow as it had been taking between 2 minutes and 24 hours for the false alarm to trigger, so it might be a premature conclusion. If so, I'll post again.

...Paul.

[PaulR]

It's the "Submit" button that does it. I swear the beep beep thing triggered the very second I submitted the last post. And now the single flash has become a delayed feature rather than almost immediate.

I reckon a trip to find a VAG Com assessment is probably my next step.

Paul.

[mylife98]

Paul, how did you do with this?

I'm currently going through the same issue with my B5 RS4.

Have VAGCOM and inital codes showed the siren to be suspect (although there were a fair few codes). Dug it out, split it open and sure enough a perfect example of the well known corroded batteries leaking onto the circuit board issue. Down to the stealers the next day for a new siren unit. Installed....

...and the damn thing still kept going off!

VAG COM this time showed only a 01369 code - Alarm triggered by Hood Switch.

With extensive torch use, I finally found the hood swtich hidden in the main hood lock, and a bit of internet research seems to indicate that I need to replace the 'F120' hood contact switch, part number 8D0959486.

I'll be ringing the stealers tomorrow to get it and will try and get it fitted in the next couple of days. Will keep you posted.

If you have any tips on installing it, let me know!

Or indeed, if you're still in need of VAGCOM, give me a shout if you're not too far - I'm based in London W2.

Matt

[mylife98]

Turns out 8D0959486 is a non-stock part - on order for arrival tomorrow. Nearly £12 with the VAT.

[mylife98]

Posting this if it helps others.

VAG COM code showing was 01369 code - Alarm triggered by Hood Switch. This is to replace the hood switch on an RS4 B5.

The part is 8D0959486. Basically a small micro switch and two small metal washers. Shown here:

http://www.mylifeconsulting.com/images/IMG_0262.jpg
http://www.mylifeconsulting.com/images/IMG_0264.jpg
http://www.mylifeconsulting.com/images/IMG_0265.jpg

The switch is hidden in the hood locking mechanism:
http://www.mylifeconsulting.com/images/IMG_0266.jpg

Difficult to spot at first, particularly if your lock mechanism is covered in years of dirt like mine. These two pictures are the same except I’ve highlighted the switch in blue in the second one.

http://www.mylifeconsulting.com/images/IMG_0267.jpg
http://www.mylifeconsulting.com/images/IMG_0267bpg


Also note the two rubber friction stoppers highlighted in red– 1st thing to do is push these out to remove the protective rubber cover for the lock mechanism so you can get access:

http://www.mylifeconsulting.com/images/IMG_0269.pg
http://www.mylifeconsulting.com/images/IMG_0270pg


Release the electrical plug from the switch. You need to depress the catch on the top of the socket fitting with a small screw driver. This shows the plug removed. You can just make out the catch on the top of the male socket:

http://www.mylifeconsulting.com/images/IMG_272.jpg

Now you need to pop off the two small round metal restraining friction fit washers which secure the switch in place. Easy to get at from the front of the locking mechanism (this photo shows them having just been removed):

http://www.mylifeconsulting.com/images/IMG_0271pg

Push the two protruding plastic retainers that are revealed (per photo 271). I had to use a pair of needle nose pliers to get the necessary leverage. The switch will pop off.

Fitting is the exact reverse.

On examining the old switch it was easy to see why it faied – large cracks and exposed circuitboard! :
http://www.mylifeconsulting.com/images/IMG_0275.jpg
http://www.mylifeconsulting.com/images/IMG_0276.jpg


Finally, clear down the VAG code and test module 35 (central locking), measuring block 001, 5th digit (1st of the second block). 1= hood open, 0 = hood closed.

Hope that helps.

[PaulR]

Hmmmm, didn't see the thread had re-started.

Same thing, VAG com showed that with bonnet closed, the switch was "chattering" open/closed/open and so on, hence the intermittent nature of the problem. With the switch disconnected signal is permanently "closed" so I have a temporary solution. Your description of changing the switch sounds relatively OK, ... so will give it go.

Thanks, ... Paul.