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There's no good reason for trying to make your own OBDII reader. There's a good bit to it. Get an ELM327 compatible reader. I strongly recommend the bluetooth versions, not the serial/USB. You end up with some funny problems, like if there is a difference in ground potential between the computer reading it and the OBDII bus, you can fry the reader.

My bluetooth OBDII reader has been great. I plug it in, or have the driver plug it in, and then I can read data from the passenger seat while we're driving. No wires required, except possibly to charge my laptop, tablet, or phone. They only cost a few bucks on eBay, and despite what you may see some brand name purists say, the generic bluetooth ones work fine.

I lost two name brand serial readers from "mysterious" circumstances (i.e., ground potential difference), at over $30/ea. I've only replaced my cheap bluetooth OBDII reader when I misplaced it. Since I spent about $7 on it, that didn't hurt as much. If it fell under a friend's car seat, I won't care if they keep it.

If you read up on the ELM327 chip , you'll see that it uses 2, 3, or 4 pins from the OBD connector for data. The bluetooth ones also use 2 more pins for power. (block diagram, page 1)

That also gives you all the information you need, if you want to code your own interface (like you would with an Arduino or Raspberry Pi.

Just to answer everything including the original post...
His remote start, door lock, etc, may be possible on some CAN bus vehicles. That's not an OBDII thing. It may be best to do those functions with good old fashion relays. I just finished decomputerizing a 1999 truck (EFI to carb conversion). It's amazing how many miles of wires are no longer necessary, and I still have all the gauges working. :) Actually, they work better than before, which is interesting. Gauges that were jumpy for no good reason are now stable and accurate. I guess there were more than mechanical issues.

http://www.elmelectronics.com/obdic.html

Check out the ELM327 chip on that page.

$33, rs-232 control of the chip and the chip speaks to ODBII: ISO 15765-4 CAN, SAE J1850 PWM, SAE J1850 VPW, ISO 9141-2, ISO 14230-4 and SAE J1939 protocols

You set the chip up with what to monitor and/or control (Similar in style to sending AT commands to a modem) and then it does the work of giving you the data stream.

Build your own standalone test gear, with or without a PC interface.

Googling for "ODB-II Connectors" was how I found the jack ends with pins to solder to. They varied in price a bit so where I purchased from 2 years ago no doubt isn't the cheapest now.

Have fun

I'm all for tinkering, and tinkering with cars used to be a great hobby. But tinkering with proprietary chip sets - with consequences not only your driving experience, but on the safety of others around you - without the proper equipment strikes me as a uniquely bad idea.

You've apparently got no understanding of what the OBD II interface lets you do.

OBD II lets you read trouble codes and operational data (sensor values, fuel integrator, ignition timing, etc.), and lets you clear trouble codes.

That's it. There's no danger at all. You can't alter anything other than clearing trouble codes.

To the original poster, google for "ELM327" to find the hardware, and "ELM327 software" to find software, including many free apps that will use the ELM interface to talk to OBD II.

I use a free app on an old Palm with an ELM327 adapter I bought off of eBay for OBD II work. Works great. I paid a little more for one that works over Bluetooth; the less expensive varieties can be plugged into an RS232 port on a laptop (old, cheap laptops are powerful enough and are more likely to have an RS232 port).

The ELM 327 is fully documented and you can write your own software to talk to it. The datasheet is here: http://www.elmelectronics.com/DSheets/ELM327DS.pdf, ELM's OBD product page is here: http://www.elmelectronics.com/obdic.html.

I'm all for tinkering, and tinkering with cars used to be a great hobby. But tinkering with proprietary chip sets - with consequences not only your driving experience, but on the safety of others around you - without the proper equipment strikes me as a uniquely bad idea.

You've apparently got no understanding of what the OBD II interface lets you do.

OBD II lets you read trouble codes and operational data (sensor values, fuel integrator, ignition timing, etc.), and lets you clear trouble codes.

That's it. There's no danger at all. You can't alter anything other than clearing trouble codes.

To the original poster, google for "ELM327" to find the hardware, and "ELM327 software" to find software, including many free apps that will use the ELM interface to talk to OBD II.

I use a free app on an old Palm with an ELM327 adapter I bought off of eBay for OBD II work. Works great. I paid a little more for one that works over Bluetooth; the less expensive varieties can be plugged into an RS232 port on a laptop (old, cheap laptops are powerful enough and are more likely to have an RS232 port).

The ELM 327 is fully documented and you can write your own software to talk to it. The datasheet is here: http://www.elmelectronics.com/DSheets/ELM327DS.pdf, ELM's OBD product page is here: http://www.elmelectronics.com/obdic.html.

Cars manufactured after 1996 have OBD-II (On Board Diagnostics). You can get a code reader/clearer for about $130 IIRC. Also, a lot of auto parts stores will read your codes for free.

You can get one for less than half that. look on ebay for "ELM327" or check out http://www.elmelectronics.com/index.html to order the chip and DIY up your own code reader.

I googled 'OBD II' a while back and found these:

http://www.obd-2.com/
http://www.ghg.net/dharrison/obdscan.html
http://www.obdii.com/ubb/Forum1/HTML/000359.html
http://www.andywhittaker.com/ecu/obdii_software.ht m
http://www.elmelectronics.com/obdindex.html
http://www.dynahud.com/default.asp

They should get you started...

With these chips, a trunk-mount 386, and Perl, I'm in the process of creating a realtime diagnostics readout for my Crown Victoria. It outputs to a small black-and-white LCD I have in my glove box. The next step will be sending spoofed voltages to the PCM to affect engine operation. Who needs an expensive reprogrammable chip? Just lie to the one you have!

And I have a better coffeepot, by the way. I got it at a truck stop. It used to plug into the cigarette lighter. I'm about halfway through reworking its circuitry to run on Firewire. Then I have to write a driver.

I was wondering, have you had any experience with third party OBD-II interface ICs, such as the one sold by these guys?

Seems there's some free software for them, too.

Just wondering, since I was thinking about giving it a shot. Might be fun to see just what I can find out about my car. :-)

I was wondering, have you had any experience with third party OBD-II interface ICs, such as the one sold by these guys?

Seems there's some free software for them, too.

Just wondering, since I was thinking about giving it a shot. Might be fun to see just what I can find out about my car. :-)