Key fob locks but won't unlock

[Pingouin]

Hi all,
A new problem developed on my 3dr 2008 Yaris this morning: although the key fob can lock the doors, it won't unlock them. I tried the spare fob, and it did the same. After many attempts, it may successfully unlock once in a while. The inside button does work though, and I can still unlock the driver's door with the key. I thought it could be the fob battery, but then the lock button always work, and unlocks is really struggling to work even when using the fob inside the vehicle. Besides, the little red light on the fob works fine.
Any ideas what could be wrong? It's still under warranty, but since it seems to work randomly, I bet that if I go to the garage it will work, they'll tell me that they can't fix something that works and I'll be wasting my time.

*EDIT* it seems that if I point the remote from the front window towards the back of the vehicle, the likelihood of the fob successfully unlocking the doors increases significantly, so I may try to change the fob battery anyway, albeit as I said before locking is working fine.

[bobolinko]

[QUOTE=
*EDIT* it seems that if I point the remote from the front window towards the back of the vehicle, the likelihood of the fob successfully unlocking the doors increases significantly, so I may try to change the fob battery anyway, albeit as I said before locking is working fine.[/QUOTE]

Shucks Auto has a keyfob remote tester on their counter (most locations) and it will analyze the fob transmitter's signal to see wheather your battery is bad/weak. For those that visit them, test your keyfob transmitter so that you won't have the same prob. I did while waiting for my reciept, and bought batteries while I was there, saving a trip for batteries. (only 2 years old)

I had the same issue and the batteries were not up-to-par and replacement corrected the problem on BOTH of my keys.....

[Pingouin]

Thanks bobolinko for the reply!
Yep, I switched the battery with a spare one I had lying around and it sorted the problem. Strangely, my other fob didn't seem to work either (which led me to believe that it wasn't the battery since I never use the other fob), and it worked when I got back home tonight :iono:
Still strange that locking was working fine. Also, the "dead" battery I removed is still at about 80% charge, so be weary that if it seems fine, it might still have insufficient juice! :eek: