I hope that someone has an answer. I've got a 98 Jeep Cherokee that has a similar problem. After I bought the vehicle, I purchased a second key fob from the dealer. Both key fobs were programmed together and shortly after, I had the same problem. Both fobs had new batteries, and thee batteries checked good by a voltmeter. The dealer replaced one fob and then reported that both fobs were transmitting. I still have the problem.

After locking the car with the remote, it will unlock if tried in a time period up to an hour. If the car sits overnight, it may not unlock. One work-around: Press the lock button and if it responds, then it will unlock.

If you unlock manually with the key, it will set off the 4-way flasher. Starting the vehicle will not stop the flashing. The work-around: Press the master door lock button on the driver's door, first to lock then to unlock.

I note that my key fobs were made by TRW.

Since you say it worked fine until you changed the battery?I would check to make sure that the battery is in secure and not loosing contact.

The instructions for changing the battery in my key fob warns not to touch the battery contacts or the contacts in the key fob, else skin oils and dirt may interfere with circuit continuity. I guess this means you should handle the battery only by by its edges.

When replacing a fob battery, "GENTLY" brush the battery contacts with a pencil eraser. This will clean surface corrosion which could cause a voltage drop and reduce the transmitters output.

Cost plays a huge role here, but even with all of the tools and equipmnent that I have I do not and cannot reasonably afford to purchase the additional equipment that would recieve signals from a key fob to measure it's output and attempt any servicing for many of those systems. We truly are limited to dealing with the components onboard the vehicle, following any appropriate service bulletins, and then if unsuccessful either leave it unrepaired, or go into parts swap mode. (Which I HATE doing, and usually would turn the vehicle away)

In order to protect vehicle security it is necessary to make purchasing the things needed to perform this kind of service expensive, that's why a dealer will have the equipment for the brands that they sell, but it is not reasonable for someone like me to get involved with beyond the level that I do.

Keep in mind some systems use the vehicles radio antenna for the key fob reception. (The radio in this case IS the reciever and communicates the command signal to the BCM). One thing that I can do with my scan tools is watch for the communication to occur between the modules. If I don't see the communication, which if the system does not unlock the doors is quite likely the result I would then do testing to confirm that the modules can and do "wake-up" with certain commands. Then from there attempt to be certain that the antenna system is working correctly, even if that means pull the radio and use a substitute antenna.

In the event the car works for a while like Jems, but does not work after a specific period of time I would suspect there is a vehicle problem where the BCM deliberatly shuts the system down to protect the vehicle battery. I would be testing that car to make sure modules eneter sleep mode at the right times, and then of course wake back up when commands are given. A radio reciever that does not wake up to the fob transmission can never send an unlock command to the BCM, likewise even if the radio does send the command, if the BCM cannot or will not follow the command, the result is the doors don't unlock.

Keep in mind, the problem could easily be a door lock solenoid failing, as well as the latch simply stiffing up and requiring to much power for the solenoid to operate.