Egr po 401
 

Yesterday, our 2006 Freestar (3.9L with 174,000 miles on it) threw a PO401 code. Today I went to check the EGR valve, and vacuum hoses. The hoses looked fine, so I pulled the EGR valve, expecting it to be clogged up. It looks really clean. I blocked the inlet to the intake manifold with duct tape, and started the engine (EGR valve off). I had decent exhaust flow from the line from the exhaust, and when I pulled the duct tape off the inlet to the intake manifold, the engine got real rough and nearly died....Good flow on both sides.

There isn't a lot of info available for this EGR system, but it appears that the EGR solenoid, EGR valve, and DPFE sensor are all inside the valve. There is one rubber vacuum hose that has one end connect to the EGR valve passage to the intake manifold, and the other end goes to what I believe is the control solenoid inside the EGR valve assembly. There are also 2 small red lines connected to the EGR, and there appears to be decent vacuum on both of them.

Am I correct about the EGR valve being a 1 piece unit with the solenoid, EGR valve and DPFE in one module? It appears that I need to replace the EGR valve....is there anything else I could check? Does anybody have any info on this system? If I knew which pin was which on the electrical I could energize the solenoid and see if I get full EGR. BTW, TORQUE shows that the EGR command signal goes higher when you rev the engine up, but the EGR error is 100% indicating that there is no EGR flowing. I've heard the engine knocking lightly a few times, and after I reset the faults, it did knock again at light throttle until the SERVICE ENGINE SOON light came on (no EGR).

After I wrote the first message, I found a site that explained that yes, the solenoid, EGR valve, and DPFE were indeed inside of one module. I also read where a couple of people had replaced theirs with aftermarket units and had them fail in about a month. I purchased a Motorcraft unit from Rock Auto and now everything is fine. When you watch the EGR error signal, it quickly goes down to zero after a throttle change.

I also found a fault in the PCM that said that the intake manifold runner actuator was jammed. I tested the circuit and found that there was voltage on the connector to the unit and also that the PCM was trying to signal it to move when you brought the RPMs up, so I replaced that also. Now you feel a definite increase in power when it gets above 3000 RPM. It looked like this fault wasn't going to cause a check engine light and was just an indication to alert you.