Does anyone have any info on hacking a reader to get the error code from the Check Engine light on my dashboard?
Depends on the car and ECU, I know on my nissan you can short two pins on the odbii plug and it will flash the code through the engine light, long flash for 10's, short flash for 1's
There are OBDII/CAN Arduino shields(like this one) available if you want to put together a custom reader. If you search this forum for the keywords "OBD" or "CAN" and "shield", you should find at least a couple of posts about people using these shields or custom boards using similar ICs to get data from their car. There are also pre-built scanner modules (like this one) that you hook-up to a PC (e.g. a laptop or netbook) and are reasonably affordable, if you aren't interested in a DIY project.