There's a connector in your fuse box.  One of the pins provides code output
for your engine computer, another for your trans computer.  Go to
www.hmaservice.com and register for an account.  Once you get your
password, go to service information, select your vehicle and the shop
manual tab.  In the fuel section, the manual should give you a good
picture of the connector and the procedure for checking the engine codes.
I've done this with an analog voltmeter and simply counted the meter
sweeps.