Troublesome EGR Codes

2001 Buick LeSabre 3.8L V6
Started off with P1404 (Pintle Valve Stuck Open), have Changed 4 EGR Valves in a Row, ALL keep tripping the P1404 Code. We Checked ALL the wiring-Nothing Detected. We Just Tried a suggestion; Disconnect The Connector at the EGR, Run a Scan, Reset, Shut-off Ignition, Re-connect EGR, and Rerun Scan. Momentarily, we Tripped a P0403 Code, then Got a Request to Clear, we did That. Service Engine Soon Light is Now NOT On.
If this Trips a P1404 again (Hoping it doesn't) what would be the Next course of Diagnostics to Determine where the actual Problem is? Having a Hard time Believing that 4 EGR Valves are All Faulty.
Is there a way to "Bench Test" these Linear EGR Valves?

I would not think you would get four bad valves even aftermarket. What you need to do is when it acts up scan the data and see where the actual and desired egr position is at idle of course will be 0% and make sure they match you may have to drive also to make sure they match then backprobe the return wire from the egr to the pcm and see if the voltage is the same. Of course if they do not match and the return voltage is correct then the PCM is not calulating the data correct. This could be a PCM upate and or replacement. If I had the VIN and the current PCM part number I can tell you about ny updates.

I agree that 4 bad EGRs is highly improbable.

On some vehicles, when you replace the EGR, the zero position for the pintle must be relearned by the PCM before the EGR will work properly.

The procedure you described did just that.

One thing that could also trigger that, is lower Exhaust Temps due to a clogged Cat. The job of the EGR is cool the exhaust gases by smothering combustion using exhaust gases. That helps to minimize NOx that occurs on high combustion temps. If the Catalytic Converter is starting to clogged up the exhaust gases can not scape quick enough.

That is worth to check.

Do the 3.8's have the port in the intake manifold that plugs up like some of the 3.1's?
If not then I'd agree in the software update and or zero pintle position may require a scan tool to reset like they said!

No jeff the 3.8 does not stop up like the 3.1 and 3.4. Dont think it is a cat problem either because if the cat was stopped up enough to hold the egr valve open then he would have no power.