2002 Impala The electric truck release isn't working. The neither in dash button or the key chain remote work. The brake light located in the center of the trunk lid doesn't work. Both stopped working at the same time. Are they on the same circuit? Which fuze should I check and where is it located? Or if I replace the brake light module will that solve my problem?

Your key needs its battery replaced so try your spare key and watch every thing work fine.

I would check the owners manual or with Cadillac - its possible the remotes lost part of the signal and need to be reset. It sounds like the receiver is not getting a signal from them by using that button.
Could be the receiver too.

try it with the key in acc position you might have a bad brake switch or bad release solenoid

Sound like a problem with the Neutral Ssafety Switch, this is located on top transmission (generally) and its possible that need some adjust.

More the nlikely your brake light switch is defective or loose.
This switch also controls the release of the shifter so you cannot shift from park unless you're stepping on the brake.
The switch is located in the brake pedal up ubder the dash.

Turn the key to unlock the the system but do not start the vehicle, shift into neutral and start, you should be able to go from there.

Check or replace the switch as necessary. Be careful though as your brake lights may also not work.

Open the trunk and check the wires near the right hinge. You'll probably have some cut wires that will need to get re-connected that go to your lights and trunk release.

change flasher relay in fuse box

there should be a red reset button under kick panel on driver side press in for 30 sec and release, that should take car of problem , also could be mount on dash on driver

The relay switch is a plug-in located inside the dash near the tach about 2 O'Clock You will need to open the dash panel to replace it and your turn signals will work.

usually in the newer impalas the bcm (body control module) located under the dash on top of the emergency brake pedal