I connected an oscilloscope to the output of the infra-red sensor (ie the
input to the central locking controller) and discovered that even when the
doors did not unlock, the sensor was still sending a signal to the
controller. This made me believe that there was nothing wrong with the
sensor but instead it was the main controller (the unit behind the
glovebox). I bought an aftermarket alarm and connected it straight into
the controller at a different point and it works 99% of the time. If
anyone needs details of how to connect an alarm, I have them.
The other interesting thing to note was that the signal transmitted from
the sensor was a pulsed signal with a very lower duty cycle.
The transmitters for these cars are very simple and it would be very easy
to make something that goes through all the combinations (not many
actually) and open the car.
To test the theory of 'recording' the signal, I programmed my learning remote
and it worked fine!
Glen Gurney
89 405 Mi16
Australia