Intermittent alarm/immobiliser issue on NB 2.5

Technical Area Electrics & ICE
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  1. My model of MX-5 is: NB 2.5
  2. I’m based near: York
  3. I’m looking for technical help or recommendations on: Alarm/Immobilisor

I have just bought a 2002 MK2.5 Sport in excellent mechanical condition, but with an intermittent alarm fault. About one in five times I unlock and open the door (on the key; I do not have a remote fob) the alarm goes off, but the car will start and drive, despite the alarm sounding and hazards blinking. So, although the issue is setting of the alarm, it is not triggering the immobiliser.

I have checked the obvious ‘plunger’ button that the door pushes in when closed, but now struggling to think of anything else. I have checked the other door and the bonnet plunger too.

Now when I say checked, I mean I have ensured they move smoothly and seem to be working mechanically, but could one of them be the cause if there is a dodgy electrical contact? And why is the alarm but not the immobiliser affected?

Or any other ideas please?

Cheers!

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The alarm and immobiliser are separate systems so don’t let that be a red herring. There is a switch on the back of the key barrel that turns the alarm off when you unlock the door, I’d guess that’s the culprit, they get water in them.

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I have a similar car but fortunately with a fob, several times I have noticed the hazard lights do not flash when using the fob because the plunger under the bonnet has been knocked askew, the metalic material the plunger is mounted on appears to have the consistency of the cheesy oxidated material much of my 1970 FIAT 128 was made of, might be worth a look to see what yours is up to.

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Cheers both.

WD40 in locks and a clean of the bonnet plunger and no more issues!

Result… :slight_smile: