I have a 2000 Dodge Neon and don't have a real OBD reader yet. The other day I started to turn my car on and, before I got to the ignition the speedometer came on with a "p" and a "1684" (the check engine light has been on for a while). I tried to get it to happen again later. I'm not sure what I did, but I eventually got it to work once but still can't reproduce it.
Does anyone know what happened and how it can be done consistently?
Edit: I would like to know how I can consistently read codes on my speedometer. I am not specifically asking about P 1684 (although tips are definitely appreciated anyway).