There are a couple of ways to do this. If you a multiple vehicles you may want to spend the extra money and get the below item to do your project testing, plus you can use it with the Scantool software and check diagnostic code on your vehicles.

http://www.scantool.net/products/pro...70eb642cf18b25

However if you have just the one vehicle the product you selected would work great. I have all five of the receivers that Elm makes. The ELM327 mentioned above replaces the ELM320-323. It does VPW, PWM, ISO, and CAN (this is new) which is the new automotive standard. The upshot with the ELM327 is that it has a standard TTL output mode, but outputs ASCII and is large compared to the ELM322. The advantage to the ELM322 is its size and it has a “packet mode” (not ASCII) option, but the TX on the chip is inverted from and needs to be “flipped” with external hardware or via software. (see datasheet)

The beauty of the elm chips is they handle the CRC, and buss timing for you. They also have packet filtering options, so you only are presented with the packets you want to see and not those that you don't. I interface the ELM chips via the onboard UART in the pic and handle everything with interrupts. (see instant interrupts thread)

Once testing is complete, you can integrate the elm chip into your final circuit board. You should be able to Tx/Rx on the line. The hard part will be deciphering the packet and setting up the ELM chip to spoof other devices. It is really designed to act like a diagnostics tool, but it may very well work for what you’re doing. I do have many of the SAE documents that I use for deciphering; however, they are $50 each. Some creative googleing may uncover the info you are looking for. I may also be of some assistance.

I have used the ELM chips for years and love them!