my check engine light comes on and I do the "3 key" check. (2007 Wrangler) It goes through the check and the Odometer displays "Done" (no code). I have reset the engine warning light by disconnecting the battery. The engine light goes off but comes back on every couple of weeks. Never has a code.
Why would I continue to get the engine warning light without a code???

 

First off, you are in the wrong forum. These forums are "platform specific" and this one is for the XJ Cherokee. You will need to post in a "Wrangler" forum.

As for determining what code, the key test doesn't work for your vintage. You will need to hook up either a scan tool or a code reader to the OBDII connector under the dash.

Some auto parts stores will do this for you (Autozone) and you can also buy a simple code reader very inexpensively. Beware though that getting the code is only job #1. Correctly interpreting that code and doing further testing to isolate the root cause is not always straight forward and can be tricky.