I had similar systems to those described here in my 1999 Grand Cherokee. It turns out that there was a bad connection at the negative battery terminal. After cleaning both the positive and negative terminals and cable ends, everything worked perfectly! My guess is that the success others are seeings after disconnecting the battery may have as much to do with re-establishing a good connection as some possible reset of the system. Lesson learned (like every automotive manual says) - always check the battery first. When in doubt, put a new battery in.