P0401 and P0403 on 99 Plymouth Voyager - circuit failure?

I'm stuck on this one, hope someone can help. I have a 99 Plymouth Voyager with 150k miles. Service Engine light is on, and has P0401 and P0403 codes (insufficient EGR and EGR circuit). Originally I just had the 0401 and I replaced the EGR valve, but to no effect (yes, the valve works -- applied vacuum stalls the vehicle, and there is plenty of vacuum from the manifold). I now have the 0403 code as well.

I'm thinking the harness and/or circuit has failed somewhere. Anyone have any idea how to check that, or any other ideas?

did the replacement valve come with the vaccum modulator that has the electrical connector on it?

HEY use a multimeter to see if you have continuity through the wire harness . Also check for resistance on egr solenoid . I have a Jendham code book that says 40-80 ohms on solenoid . If you have your own manual double check the resistance .

Thanks for the suggestions --

Yes, the replacement has the solenoid w/ connector, I went ahead and bought the whole unit.

I have a Haynes manual and just checked the wiring diagram -- looks like it won't be too difficult to check continuity of the circuit, it is pretty simple. Power from the PDC, with a ground signal from the PCM. I'll give it a check.

Some sources have referenced a differential pressure sensor or similar as a possible point of failure (esp. for Fords) but I don't see any similar sensor on the Chrysler. . . but I'm a little surprised there is not some type of feedback mechanism to tell whether the EGR is working -- or am I just missing it?

Marc

the vaccum modulator is the feedback, the pcm sees that it closes and looks for the change in oxygen content with the 02 sensor

That makes sense; I thought it must be something like that providing a feedback, since there is no sensor indicated anywhere.

I will check the continuity of the harness and try and clear the codes and see if that gets me anywhere.

Thanks everyone; let me know if you have any other suggestions.

Just to tack on the resolution . . . turned out it must have just been the faulty EGR valve and nothing else. I had expected the system to clear itself after I replaced the valve and did some drive cycles, but it didn't, so I suspected something else going on. I ended up borrowing a hand-held reader and cleared the codes manually. All is well. I did some driving since then, and even got my CT emissions test done (an OBD test) and everything was good. Thanks for the help, everyone.