EGR Code 406

[Gapper_ca]

Replaced both EGR selinoids Red and White. Code comes up as 406 EGR valve high voltage... reset ECU and on second start codes comes back. not sure what to do? trace back wires for EGR ?

[Gapper_ca]

well after another trip to local mechanic, and some more testing found out that the vacum pump was poor. only got 5 lbs boost just enought not to thro a wastegate code but not enough vacum to operate the EGR valves... so a quick call to a local wrecker, and a new to me vacum pump for $100 vs $350 new.... and all codes gone and lots of boost...
damn nightmare trieing to figure this one out. EGR codes but a vacum pump problem...

[gmctd]

PCM has no way to read actual EGR, having no O2 sensor(s) - PCM controls EGR by regulating vacuum to the EGR valve actuator - PCM measures the amount of control vacuum with a MAP-type sensor on the firewall - you may have noticed the tubing from the EGR Vent solenoid.

Vacuum at the pump should be 26"hg at idle and 2000rpm

Vacuum on the EGR varies according to demand, but should be 0" at idle and 2000rpm, engine unloaded - EGR is used in decel and excess loading event, when cyl temps are too high for acceptable emissions.

[JohnC]

I'm not sure how good a deal $100 for a used pump is, but $350 for a new one sounds awful high...

JD - the later trucks have a mass air flow sensor that is instrumental in evaluating the egr flow rate. Much harder to trick than the earlier ones.

[gmctd]

True, JohnC, tho there are codes for the MAF sensor, even for being dirty.

Still boils down to how much vacuum is available and on the EGR\MAP, as regulated via the EGR\Vent solenoids

I 'spect the MAF is really there to reduce airflow, preventing hi exhaust pressure from blowing the EGR valve open - we've proven that, fer sure.