P0401 EGR Flow Insufficient

TrixEclipse said:

So I've been struggling with this problem for a while now and I don't know what else I could possibly check in the EGR system. I know there's been a million threads on EGR problems but I've been looking through most of them and all they say is "just clean EGR" or "Replace EGR" or "check your sensors" and I've literally done all that and can't find a single problem. My car is a 2003 Mitsubishi Eclipse Spyder GT 3.0L V6 with Variable Induction Control. My problem seems to be that the solenoid is not engaging and producing a vacuum, it remains off and allows air to flow through without allowing vacuum to EGR valve.
So far this is what I've done:
- Replaced vacuum lines
- Cleaned EGR valve and intake and exhaust ports
- Checked EGR valve by supplying vacuum at idle (RPM drops significantly = no clog and EGR works fine)
- Checked EGR solenoid (terminals are being supplied voltage around 5V at cold idle, continuity is within specs around 33 ohms, hooked up solenoid to 9v battery and it turns on and closes to hold vacuum)
- Checked Manifold Differential Pressure sensor (backprobed while engine on at idle and it is being supplied voltage)
- Checked vacuum lines running from EGR solenoid to vacuum control valve and EGR valve (all lines are good and hold vacuum and are cleared when blowing through them))
- Ran a live systems check using BlueDriver OBDII focusing on the coolant temperature sensor and it ran fine (start was 78 degrees outside temp and engine read 84 degrees, warmed up slowly at idle to 184 degrees and stayed there)

Does anyone else know of any other component in the EGR system that could alter the flow of vacuum? Maybe some other sensor that would fail and not tell the CPU to turn on the EGR solenoid? Or maybe even vacuum within the intake manifold itself? I took it to a shop a while ago and they said they tested for intake manifold leaks and could not find any so that shouldn't be it. Let me know if anyone has any ideas please.

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Murkrow said:

Sounds like the vacuum port on your throttle body is not providing vacuum to the solenoid.

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Eclipse-GT said:

Not sure if it pertains to your specific issue but wanted to toss this out there for anyone interested.

On the passenger side of the motor, top left, one of the vacuum lines has a small piece of foam (I believe it's foam) and most either don't know, diagrams don't commonly show it, hose is replaced and new one doesn't have it in, etc causing issues. Don't lose that piece within the vacuum hose. It's required.

I can't recall if that's egr related, but I'm fairly certain it is.

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