Sounds more likely that the internal contact on the fob"s "Lock" button
has died. Doe you have another fob that you can check against?

The setup is like a universal TV remote -- if you lose the programming
for one (VCR), you've also lost everything else (TV, stereo, DVD...)

Does the car have an alarm, and is that activated when you press lock?

Niels

The door lock receiver is to the right of the glove compartment.  If
the evaporator was replaced (dash disassembled), then it's a
possibility.  

Otherwise, it may be the same problem I experienced (and fixed)
recently on ky 94 wagon.  
Try this:
With the doors locked, unlock each door (and trunk/tailgate) with the
key,  If, after unlocking it, both remote buttons work, then you have
the same problem I had.  (Description and repost below).
If unlocking that door has no effect, lock it again and move on to the
next.   (Not sure how this would work with the keyless reaar doors
though.)

**** REPOST of 4/29/05 message ****
One day, I noticed that the tailgate didn't lock when I locked the
rest of the doors, via remote, or key.  So, I locked the tailgate with
my key.  

Some time later, I noticed that the remote was NOT locking the doors.
I could unlock, but I had to lock it via the driver's door key, which
also locked all the other doors (except the tailgate).  The spare
remote exhibited the same behavior, so the problem was in the car.
If I used the key in the driver's door, every other door except the
tailgate would lock and unlock with it.  

Some initial troubleshooting revealed that, if the tailgagte was
manually unlocked, then the remote would both lock, and unlock the
car.  

I pulled the tailgate latch assy, and noticed that the seam of the
plastic motor housing was split open along the plunger side. (arrows
in this photo:
http://webpages.charter.net/dwarner2/LockFull.jpg  
I wish I had remembered to phoograph the innards, but the way is works
is that the motor (in the left side) via reductrion gears, drives a
coarse pitch that runs up the middle of the plunger.  
The screw engages a sliding block that travels between the plunger
legs, and carries it up, or down via spring loaded detents.  It
releases it's grip on the plunger at the end of it's travel in either
direction, so the key lock is free to move the plunger as well.

At the bottom of it's travel (unlocked), the plunger activates a
switch, that signals to the central locking relay that it's locked.
When it's up, an "unlocked" signal lead is grounded instead..  

The casing was split along the plunger side, apparently keeping it
from actuating the switch properly.  When unlocked, it was still
signalling the lock relay (which contains some logic) that the rear
door was locked, while the other doors were grounding the "unlocked"
signal.  Receiving both "locked" and "unlocked" signals prevented the
locking relay from responding to the input from the remote receiver.  

When the tailgate was unlocked, the relay still received mixed signals
in the opposite direction, but somehow, this didn't prevent it from
operating.

I tried gluing the housing with cyanoacrylic cement, but it split open
again on the first cycling of the remote.  So, I re-glued it and
reinforced it with shortened staples sunk into the plastic with a
soldering iron, then secured with some more glue.
http://webpages.charter.net/dwarner2/Stapled.jpg
Looks messy, but it's worth about $300 to me :-)

I think that the motor had a bit of overrun, and when the drive block
ran into the stop, the remaining torque worked to split the casing
open.  

It works fine now.  And, I've finally removed the loose tailgate liner
so I can repair the clip anchor holes.

-----------------------------------------------------------------------

Also, the receiver has only four connections, 12V, ground, ignition,
and output, which is pulsed differently for lock and unlock remote
functions, so, if works one way, then all the wires are connected.  

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