RAM is a acronym for Random Access Memory. It's refering to a problem with the ECM (Electronic Control Module) that's on top of your engine. It would be best to take it to a dealer and have them see if you have a ECU issue or if the code is being generated for some other reason. The manual states that code P0604 can possibly be caused by "electronic noise" due to non-OEM electronic parts (coils, injectors, etc.) being used on the engine.
Hope this helps, DAWG