Looks like the hardest part is to get a cheap ODB2-RS232 converter.

But this seems to be the solution:
http://www.elmelectronics.com/Products/Connect/Connect.htm
I'll order one and let you know how far I get.
(BTW: I drive a ford, so I'll use the PWM version.)

By looking at their sample app (see pdf) this shouldn't be to hard at all...
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