2003 Ford Taurus and the check engine light just came on Can you run a self diagnostic by turning the key on and off in a certain sequence like you used to do on an older model Ford truck?

Answer 1

1) no

2) it's OBDII. Most parts stres will read the codes to you (and clear them) for free. You can also buy a reader for very little.

About half the Check Engine light problems on these tortioses are caused by a loose gas cap, a bad ignition coil, or a bad DPFE sensor. If you're a DIYer, keep that in mind after you get the codes read.

If you have access to a scan tool (not a code reader) you can use the DPFE PID in the data stream and a vacuum pump to test the EGR system, and you can use mode 6 test ID 0x51 or 0x53 to identify any weak coil.

Most EVAP faults not related to a loose cap are caused by a bad o-ring near the canister easily identified using a smoke machine when the car is nice and cold.

If you get a cam sensor code, consider if you've been hearing a squeak noise like a belt chirp that doesn't go away when you replace the belt. If so, use a prybar or similar tool to press down on the synchro. If the noise goes away replace both the sensor and the synchro.