Hi All,
I worked on my 2004 X5 3.0 all week, replaced the front left drive shaft, and also replaced the amp which had become defective due to known issue of moisture coming into that area. I had disconnected the negative terminal on the battery while I was working on the amp. When I reconnected the battery the car started doing all kinds of crazy stuff lights going on and off, alarm sounding momentarily. I quickly disconnected the negative side. check battery voltage and see that it needed a charge. So I charged overnight. When I reconnected battery everything lights up as normal all sounds good and turns over well but no engine start.
Here is what I have diagnosed so far:

Checked codes and found P0604 Internal Control Module Random Access Memory (RAM) Error
This code was probably left from the dead battery. However I cleared the code and now no codes come up what so ever.

Checked all fuses related to fuel and ignition
Checked Fuel pump relay Confirmed that Fuel pump is working and there is fuel on the rail under pressure
Went ahead a replaced the battery
Checked for any bad wiring or corrosion

I am beginning to think it has something to do with the ECM or imobilizer. I know for this year there is no IBS so there is no coding needed for a battery change.

I have been reading this forum and found nothing to lead me in a direction of solving this issue. Any ideas would be much appreciated. I have been reading your forums for years and have gotten alot of answers to date. Became a member today so I could participate finally. I love my X5 and the 2nd owner with 185,000 miles I plan to drive this car until the wheels fall off.. Thank you in advance for any troubleshooting advice any of you could offer.