I just started getting this code....From what I read it is reading below 0.25V enough to set the code.

I have also noticed a very slight smoke at idle....maybe just cold.

Truck runs good but my question is: What is this circuit? Has this been seen before?

Is it a failure in the circuit or the sensor?

Truck is a LB7 2004 with about 38K miles.

Any thoughts would be appreciated.

The EGR vacuum sensor is used to monitor the amount of vacuum that is available to the EGR Valve.
I would start with checking the vacuum tubes between the pump and the EGR valve.

To quote the manual " The EGR vacuum sensor is used to monitor the amount of vacuum that is available to the EGR valve. A low reference circuit, a 5 volt reference circuit and a vacuum sensor signal circuit are used to interface the ECM with the EGR vacuum sensor. If the EGR vacuum sensor signal voltage is pulled below a calibrated value, DTC P0405 sets."

Diagnosis centers on intermittant, shorted, open connections to the sensor, a bad vacuum sensor part or a bad ECM.

Should still be under warranty, looks like a trip to the dealer.

Alan, WanaDmxsub thanks for the help....yes ANOTHER trip to the dealer.

It sounds like a short circuit problem.