Received code P0401, EGR flow insufficient. Is there anything besides vacuum lines or the EGR valve that can cause this?

 

There's a solenoid that controls the vacuum that in turn powers the valve. Might want to check that.

 

Correct. As a matter of fact they replace that along with the valve as part of the replacement part. I think that is what it was. I just warranty exchanged the one I replaced last spring. (It had a 2 yr, so I was pleasantly surprised!) The valve itself appeared to function correctly. It drew back and held vacuum. But the control solenoid you cannot check readily, as it only comes on when the glorious computer tells it to. I don't know if it is activated by 12v or if it is stepped down, so I didn't mess with it given that I didn't want to futz up my warranty coverage.

We'll see how long the replacement one lasts. I hope that is all there is to it because that way I don't have to spend more $ on it.

Thanks.

 

Well, that didn't work. As soon as the EGR system kicks in (Highway driving, of which this car gets little) the light kicks on, P0401. Today however, when it did kick in, there were 2 pops at freeway speed, cruising. (Initially I thought it was something in the road that I ran over, but the light came on within seconds.) Never heard those before from this car. That is the only code displayed.

Does anyone know which sensor, or combination of sensors determine EGR flow for the computer? Perhaps the IAT or MAP, or O2, or a combination? The 4 - O2 sensors have been replaced within the last 2 years. The IAT, MAP, TPS, etc have not.

 

During normal operation, the computer uses input from the MAF (mass air flow) sensor, the ECT (engine coolant temperature) and CKP (crankshaft position) sensor to determine EGR control.
Periodically, the computer actually shuts down the EGR system in order to test its operation. It then monitors the O2 sensors looking for the expected changes. If it doesn't get what it expects, it will set the P0401 code.
Problems with all those sensors should set their own error codes, however, so I don't know if that is going to help you.
Are the tubes clear? I can't imagine how they would get blocked.

 

I haven't checked the tube, but I can't see how it could plug up. I'll pull it just in case.

The Crankshaft position sensor was changed out last year. Forgot about that one.

If any other epiphanies strike someone, I'd appreciate it.

I can run it around town for weeks without the light coming on, it's only at highway speeds that this occurs. It seems to happen every time it hits the freeway/highway. (I live in mountainous rural country, nearest freeway is 20 miles away, so I don't hit it much.)

I guess I'll check the operation of the other sensors, even though they aren't throwing codes. Maybe a sensor is only failing in one area, and maybe I'll get lucky in finding it.

Thanks for the direction.

 

Have you changed your exhaust system? Could it be that insufficient back pressure is causing the EGR to be starved at high speed? Just speculating here.

 

No. (Never would have thought of that.) It is stock and does not leak. It appears intact and sounds exactly how it always has. Any way to test it?

 

replace the EGR valve

 

Finally figured it out. Even replacing the valve didn't help. Why? Because the valve is actually assembled upside down when you get it from the manufacturer. The bolt pattern is correct, but the ports are reversed. (Intake in center, Exhaust to the wrong side)

I flipped the EGR valve over, replaced the vacuum lines to the controller with longer ones, mounted it all, and it finally works just fine.

I have informed Autozone of the difficulties with the part, but rather expect them to not care much.

Thank you all for your attempts to help. Actually they did, but I never would have expected this.