The seemingly classic MK2.5 alarm issue

My recently purchased mark 2.5 sport has developed the “alarm goes off even with the key” issue and while I’ve read lots of threads on what the problem is (Lock barrel Microswitch), I’m still a bit confused about which one needs replacing and how it relates to the behaviour the car is displaying.


The central locking does not work when the car is locked or unlocked from the passenger side. Diagnosis: Switch in passenger door probably isn’t working and needs replacement.

The Central Locking does work, in both directions, for the driver’s side. Diagnosis: this switch is working.

Locking the drivers door with the key also arms the alarm and the dash light starts flashing. all good.

Unlocking the drivers door with the key triggers the alarm, but also unlocks the passenger door.

Alarm cancels by opening the boot from the key.

My understanding is that the same switch on the lock barrel both arms/disarms the alarm and sends the central locking signal to the other door. So I’m kind of stumped as to which switch to replace. the passenger one is clearly not working, but the problem is triggering on the drivers side…

Thanks in advance…

oops, please delete…

I’m no expert on alarms, but some basic questions will clarify any thoughts I have.
!) Don’t you have a remote fob?
2) which key are you using, the plain steel one, or the one with a plastic end cover (the correct ignition key)
The plain steel key (intended as a spare,) using it to lock doors will work, but not allow door unlocking without setting the alarm off. The original coded ignition key will allow both conditions. The remote fob works as well, and saves the inevitable door scratches from using a bunch of keys instead.
From you list of actions (symptoms) it sounds like the passenger door switch needs replacing and there’s nothing amiss elsewhere, but Rhino is the expert, and I’m sure he’ll have some wise words after me.

The Mk2 only had a microswitch on the drivers door lock. Did that change on the Mk2.5.

Was there an alarm fitted as standard on the Mk2.5, plenty I have worked on did not have a standard alarm.

Answer to top item is yes - IF the alarm system is fitted.

Bottom point is open to question, I need my equipment brochure to check, and I can’t find it at the moment. Alarm is on my car, but it’s a Sport edition. Alarm, remote switching, immobiliser - the works. It’s possible the OP has a non OEM alarm, but I can’t confirm that either, but if he has no remote switching (key fob) then it may be aftermarket. Alarms are in a supplement manual, including sat/nav, but very little useful information, unlike the normal wiring manual. The circuit diagram is in block form only, showing  some components as an empty block, and allied switching shown separately, bot no clue as to looms, connectors en route etc. If I find the equipment brochure, I’ll come back, otherwise I await Rhino’s input.

The car didn’t come with a fob. I think remote unlocking may still have been an option, rather than standard on a 2004 car. My previous Mark 2.5, a lower spec 2003 1.8, had a remote fob, but it was a toad aftermarket job.

i have looked at the Haynes and will look to see if there a remote unlocking receiver in the footwell tomorrow, but need daylight for that- if there is one, then ill Try and get a fob (seen the instructions to pair it to the car)

Im using a plastic- ended key. Both keys that came with the car are identical.


I have the wiring diagram for the Mk2 and Mk2.5 including the one for the final Mk2.5. I dowmloaded them from the Mazda portal. I will have a look and see if it is on the wiring diagrams but it may well be that Mazda UK fitted them at the docks in the UK.

But your car list shows an SVT Sport? - All 1.8 models had SVT (or VVT, to be correct.)

It’s definitely the factory alarm (or theft-deterrent system as the handbook annoyingly says)  from the way it behaves when It arms (flashing dash light) and goes off(horn for 25 seconds, flashers for 5 minutes)- it’s exactly as described in the handbook. 


Alarms were fitted (not necessarily with keyless entry) from February 2001 production.

Your problem to me sounds like a micros switch fault On the key barrel. That disarms the alarm, the central locking is activated by the door lock link switch in the door lock mechanism, the same as when you lock the door using the internal lock lever next to the release handle. By design, I don’t think it should central lock from the passenger side.

Thanks, everyone. Ordered the switch, will do the job next weekend. Until then, it’s running round the car in the morning so as not to upset the neighbours.

Hi everyone! I find this forum more than helpful but am stumped on this occasion (have read all of the above without fully understanding), so this is my first ever post.

I’ve had my 2003 1.8 Sport from new and was of the understanding that it didn’t come with a factory fitted alarm but an immobiliser instead. Or are they one and the same thing?

Anyhow my neighbour has advised that the car has been beeping and flashing its lights on more than one occasion whilst I’ve been out. I’ve not had any modifications installed so a) does it have an alarm system, and b) what is the likely cause?

Ps I’ve never changed the battery in the key fob as it still appears to work fine - could this be a potential cause?

Thanks in advance!