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300TDi Alarm Woes


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I've a 300TDi, 1996. Owned it for near on 8 years and apart from a minor hiccup with the alarm spider during the first year of ownership it's proven to be supremely reliable.

Recently however, the alarm has been driving me and the neighbours insane.

It's suddenly starting sounding at all times of the day and night and 4am Monday morning was the last straw.

The car has a two button remote and I've replaced the battery in it. It always locks on the first press and always unlocks when required.

Recently though, the alarm will often sound as soon as the doors are remotely locked and will silence when re-opened. Relocking often seems fine but you just know it won't be long before the alarm activates of it's own free will, sometimes 5 minutes later often it's hours later.

I've disconnected the interior volumetric sensor so that's out of the equation but the problem persists and now I'm stumped.

I've also unplugged the standalone sounder just to appease the neighbours but obviously the hazards are flashing when the damn thing goes off on one.

If anybody can offer any advice I'd be very grateful because I'm on the verge of dropping a match in the tank and walking away!!!!!!:wacko: :wacko: :wacko: :wacko: :wacko:

Somebody........please save my sanity!!!!!!!!! AAAAAARRRRRGGGGGGHHHHHHHH!!!!!! :angry:

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Hi Underdog,

I've got a 200tdi (yes i know, before i get jumped on, its a completely different system) with a 1 button remote that worked absolutely fine for the first 16 years of its life then with not apparent warning decided to give me the complete run around. there was no end of insanely annoying faults ocurring in a completely unpredictable manner, from false activations, to not unlocking, to not locking to the immobiliser staying on. all these problems developed really quickly after the 1st fault reared its head. only a new alarm module solved the problem (on my truck it was behind the steering column to the left of the fuse box however something leads me to believe that yours is in a kickplate somewhere?, someone on here will know) and now a 17 YO disco is now very well behaved again. what i'm trying to say is that there maybe much more knowledgable people out there that can correctly diagnose your module fault or maybe even fix it for you when in my honest opinion and it is just my opinion that £20 quid on e-blag for a new (secondhand) module and a set of programing instructions from on here somewhere will cure your fault and save much time and headbanging. i did it £5 plus £1.99 postage for my AMR 2103, after weeks of typing,phonecalls and pulling my hair out i so wished i'd done it sooner.


p.s. the model number of your module is written on it, locate it, read it and google it, straight swap!. :rolleyes:

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Mine was doing the same...same age, same spec..double check the spider...if its still on...it could be broken solder joints. 6 had failed on mine....soldered them and all others just by reheating them....shoved it back and been fine ever since.

Mine was also imobilising so I had to do it...it affected the alarm in same way as yours...intermittently


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As I mentioned in my initial post, I did have a problem with the spider some time back, so long ago that the photos used in the Definiative Alarm Spider Post on this very forum, are in fact my own pictures when I resoldered the spider in the current problemsome vehicle. I am happy that this is not a Spider issue and relates solely to the alarm but I could be wrong on this.:angry:

I have recently charged the vehicle battery to ensure this wasn't causing a voltage drop issue which the alarm was seeing and sounding off.

I have larruped everything around the door pin push switches with WD40 but the problem persists.

The alarm module is in the passenger foot well so I believe, and this is next on my list to examine.

The problem started prior to the more recent wet weather too so I'm not convinced it's a water ingress issue but being a Discovery...........this is always possible. :(

I understand that the alarm module cannot be reprogrammed on the 300TDi ( 2 button remote ) like it can on the single button remote and requires specialised programming and the inevitable jumbo slug of cash to resolve, so I doubt it is a straight swap but I might be wrong. :huh:

One thing that has always been a feature on this vehicle is, if I press the remote before all the doors are closed the alarm immediately sounds. Since this problem started, one of the symptoms has been immediate sounding of the alarm upon vehicle locking. Now I'm guessing here, but doesn't that suggest the alarm is seeing a door open even though they're all closed?????????

I'm going to remove all door pin push switches, check the contacts and refit, then check nothing has come adrift with the module and make sure it's all plugged up.

I've trawled the net visiting dozens of alarm related posts and this is definately a grey area with symptons being varied in the extreme.

I'll report back if I find anything. :unsure:

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Interesting you should say that Andy, I'd read elsewhere that 2 chirps is normal but mine has always sounded the alarm if something is not closed.

It would also be interesting to learn if a 96 300TDi can be plugged into a computer to read off the last alarm trips? Does anybody know if this is possible?

I'm really hoping I'm onto this as it is seriously doing my head in!!!

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However if you had a door swtch problem you'd have the interior light coming on too wouldn't you?

This is exactly what I'm thinking. I'm thinking along the lines of, alarm gets armed, some time later a door contact shorts to earth and the interior lights come on, the alarm sees the voltage change and off we go again waking the neighbours up!!!

I have now been and checked all the push switches. The rear nearside door ( it's a five door BTW ) switch attachment screw did seem rather slack but I'm not sure that would cause a prob. Rear offside was covered in fluff but again same applies.

I've also had the passenger footwell panel off and have made sure everything on the alarm module is fully plugged up, it was dry too, no damp anywhere there.

I'm going to plug the standalone sounder back in during the day over the weekend to see if the problem is still there.

Can anybody add anything about the the MFU and test mode please?

If anybody can add anything to this, even if they think it may be trivial, please speak up as you may hold the secret to this mystery. :rolleyes:


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I seem to recall that you can unplug the siren on this alarm system and the rest of it (central locking etc) will work with no problems.

if am right this will at least allow you to find the fault with out waking the neighbours smile.gif

My memory may be a bit flaky on this as it is a few years since I had my Discovery (also a 1996 300TDi)


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Five minutes on a Testbook or equivalent will show you the cause of the last five (I think) alarm triggers which are stored in the 10AS alarm ecu, from memory I think the possible causes are drivers door, other doors, ultrasonic, bonnet or key on.

I'd do that before you waste any more time, it will show you if there is a single cause for each alarm incident or whether they are all over the place in which case I'd suspect an alarm ECU with personality issues.

Also bear in mind that the switches make an earth to the 10AS so a chafe in any of the switch wires might create a "door open" signal.

I'm puzzled about the alarm sounding when you get a mislock condition, it should not do this you should get a "bip bip" and then when the mislock is cleared, it should arm and flash the indicators three times. What happens if you open everything and try to arm the alarm? If the correct mislock indication is there (two beeps from the horn) then shut each panel in turn and if you get one that then activates the alarm, it might indicate a bad connection or chafe on that circuit as it is "shut" one minute and then "open" = alarm goes off.

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Thanks for the responses guys.

I'll need to find somebody with Testbook I think and see what this says.

I've had the bonnet switch off today and cleaned it up but it was pretty good tbh.

The alarm sounding during mislock has always been this way, I know not why, I have never heard the two chirps.

I'm getting the three hazard flash on arming which I know is normal.

Next on the agenda is to remove the vehicle battery for a while and hope the alarm "forgets" what's giving it these issues.

I know, I know, clutching at straws but desperate times and all that!!!!!!! :rolleyes:

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I have had a problem with battery drain on my 95 300tdi so i have removed the alarm relay from the passenger side footwell to see if this is the problem,the indicators don't flash anymore when i lock it. Although i know it isn't protected by alarm anymore may be worth you taking yours out until you can get it tested.

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