2005 R/T, 196K, stock, no mods.

I suspect this might have been addressed before, so if anyone knows where I can find it, much appreciated.

Just this last weekend I got a check engine light. I did not have a reader, so I did the ignition on/off/on/off/on diagnostic and the code that came up was P0604, no other codes.

So, first thing I did was disconnect the battery to see if the code would clear. It was still there.

Reading around about it, sounds like this code by itself is not usually an emergency and there are other things to try. But it also called this code a "cat and mouse" code, gotta love those. But, here is what I thought about doing:

1. Hook it to a reader just to make sure there are no other codes. Could there be codes hidden and not reported by the ignition "trick"?

2. Disconnect battery and pull the 11 and 17 fuse. Read somewhere one of these controls the computer memory, but was not clear which. But regardless, this should, I would think, clear everything.

3. If it comes back, check the battery. Battery is at least 4 years old (how long I have had the car), and I read somewhere a dying/failing battery can throw this code.

4. If not that trace some wiring and see if anything is in bad shape. Any ideas or diagrams on what lines to trace?

5. If not that, look into a replacement ECM. One from Mopar seems to run $800-1000!? Looks easy to install and I have found remans for about half of this or less. Anyone got a suggestion on a reputable reman ECM seller? Also, is it required to get it flashed to my VIN, mileage, etc?

Thanks,

Troy