I am assuming here that the spare key is roughly the same shape and
size as the one with the buttons. The old system used by Pug used to
rely on IR codes to disarm the immobiliser, they now use a chip in the
key that is read by the car.  The car asks the key  for its ID as part
of the start up procedure. No battery is needed in the key for this
just a chip that is activated when in range. The buttons on the key
merely work the central locking.

Have you ever used the spare before? I suspect it has never been
programmed to the ECU. If you have had the car from new you should
contact your Pug dealer to find out which keys have been programmed to
the ECU. This is what Pug recomend you to do when you buy second-hand
to check that there are no extra keys out there. If it turns out there
is only one key programmed I think you have every right to complain to
the dealer who sold you the car in the first place.

Of the 3 keys we have, 1 has a button to do the central locking, but the
other 2 have no buttons, cannot be dismantled (single casting of
plastic), however they do have small chips in them which are used by the
immobiliser system.  There's a coil near/around the ignition lock which
energises the embedded chip and then gives it's ID to the system.  If
the ID is in the ECU then it disables the immobiliser.  If it's not,
then the starter will turn, but the injectors/pump/spark plugs or
something don't work, thus stopping it from starting.

The history was when we got the car (2nd hand from a Pug dealer) we only
got 1 key (the button one).  We therefore asked for a 2nd key to be
provided and programmed free.  A few weeks later we got it but it wasn't
a button one for the central locking - queried this and they said this
was standard due to the cost etc.  Fine with me.  Then a few
weeks/months later they sent us another key saying the original seller
had found their spare key and given it to them.  Tried it in the car and
it did everything except start it.  When asked about it, they explained
that only 2 keys could be programmed into the ECU and therefore this one
had been disabled.

That's why we have 3 keys and only 2 work, even if it doesn't have a
button/obvious electronics in it.

D

Your dealer is telling you lies.

When new, your 406 had *TWO* electronic keys - both identical, and both fully
functional.

As you've found out, a "spare" key with no electronics is a complete waste of
time ... someone somewhere has your second "real" key.

Or save your money and DIY:

http://www.peugeotdiesel.com

As for Dave G via CarKB... I think the second key that you have is one
without a transponder inside. It doesn't need any other electronics e.g.
buttons as they are just central locking or boot release on Pugs. But the
key does need the transponder and it does need to be coded to the cars ECU,
is there an extra plastic block or glass container with some electronics
inside it in the keyfob? That will be the transponder, failing that as one
person has said, just use the spare key in the ignition and hold the
original key close to the steering lock when you start the car.

Chris

I think you have me wrong.  I was wondering if the part inside the cowling
that reads the key, reads it constantly.  If it is only required to start
the car, then putting the plip key next to the non-plip key might send a
signal to the immobiliser to disarm, thereby using the normal to turn the
lock and start the engine.

The only thing you might have problems with would be alarm systems which are
activated and deactivated by the remote plip. Opening the door with the key
in the lock could in some cars cause the alarm to go off.

Yes you are correct and it works very well providing the car knows there are
2 keys .. very expensive if it dosn't.

DaveG