How do you repair code p1409 on ford 250 van 1997 year model?

EGR vacuum regulator circuit fault

This means one of the following:

The EGR vacuum regulator solenoid has failed.

The EGR vacuum regulator solenoid is unplugged

The EGR vacuum regulator solenoid has a faulty wire between it and the ECM

Or There is a faulty power supply or ground in the this circuit, commonly a hidden splice in the wiring harness.

Or the ECM is bad

First you need to prove the regulator is good with a OHM Meter.

Then you need to prove the wiring between the Valve and the ECM is good.

Then you need to prove all the power supplies and grounds are good to the ECM

You will find your issue during this testing and if you have done your testing correctly and found no problem the ECM is bad.