I'm working on the 2004 Jeep Grand Cherokee 4.7 showing error codes

website https://big-manuals.com/products/copy-of-jeep-grand-cherokee-xj-yj-1995-workshop-service-manual

and this book helped me repair it within an hour, all by myself!!!! It's amazing, no hassle at all
From wiring diagrams, schematic illustrations, spark plugs info, parts info, stepwise instructions, torque specs, error/fault codes, engine info, to every single minute parts, you get everythingg in there you can't imagine how detailed it is

that is the PCM, you are scanning,,, you never said .
it means the perminante memory in the controller is scrambled.
is this a 2004 libertry or a 1995 GC?
the 2004 the trans brain is inside the PCM now.
so what is 12? that is olden days codes, not 2004....
tell the full story,, (symptoms) so i wipped out my OBD2 scan tool
jacked in to the PCM and ......???????
that?
if you get checksome errors)
1: low battery voltage, parked key off is 12.6v, if not charging issues.
2: PCM bad, pull battery cable, minus, wait 5 min, then put back.
the memory can read corrupted for 3 reasons
1: low battery
2: memory is bad. (vast reasons inside)
3: PCM is bad.

Ask for a free scan of your computer at any chain auto parts store; there is probably an error code stored that may tell you the source of the problem. It takes only a few minutes and will yield a 4-digit code pointing toward the problem.
I suspect the idle air control is faulty or you have a broken vacuum line or leak.

go to your local auto parts store and have them read the code most auto parts stores read the code for free

some of the auto parts stores like autozone will check the code for you for free so you don't have to buy a scanner.

usually it is behind the driver side head light but this code usually means either the gas cap is bad or just left off or loose

Have you diconnected the battery for 20 min to reset the puter?

take vehicle to a major auto parts store, most of them will pull codes for you for free

Look for noise in the TPS circuit that can cause TCC to lock and unlock.

yes autozone can tell you what the code means wether it is internal or external