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Does anyone know how exactly the eec detects excesive or insuficient EGR flow? There are no sensors on the valve itself so I dont see how... Anyways... any imput would help.
 

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That is the exact DTC I got when the vacuum tube came off the EGR valve itself. I had put the tube over the main manifold vacuum tubes, and the vibration must have loosened it.

To answer the question- The computer controls the EGR valve by method of a electronic vacuum switch. When the engine needs EGR, the computer opens the servo, letting vacuum get to the EGR which opens the diaphram.

The computer will send an EGR signal if the mixture is running too hot, or if the mixture is so lean that it needs inert gasses. If the signal is sent, but the mixture doesn't richen up or cool off, the EGR must not be working right. Hence, the CEL. The O2 sensors detect all of these conditions.

Hope this helps,
 

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Sorry, but you are both wrong ... sorta. Dan, the hose that came off the top of the EGR valve itself is what accuates the valve. The "sensing" of when the system should actuate the valve is done by a "hidden" sensor assymbly called the DPFE, which stands for "Differential Pressure Feedback EGR". This sensor is bolted to the side of the engine, below the EGR valve. If you are under the car and look at the rear bank of cylinders and find the EGR sampling tube off the rear exhuast manifold, follow that to where two hoses connect to the EGR sampling tube. These two lines go to the DPFE and are used to measures differential pressure either side of the venturi in the egr tube to check flow.

If flow is detected the ECU then decides if the EGR system should be actuated or not. Of coarse, there are other parameters that over-ride the EGR sampling, like if the car is at WOT or ideling. The DPFE has an electrical pigtail that plugs into it that sends and recieves commands to and from the ECU. The ECU tells the DPFE when to sample, and the DPFE reports it's results. The ECU does the rest. If the car is ideling or at WOT, the ECU does not request sampling values from the DPFE.

What often happens is that carbon buildup will clog the tubes, thus not allowing pressure to be sensed, thus throwing the DTC and subsequintly the CEL. Also, over time, the DPFE sensor goes bad for one reason or another and will not detect it's parameters, thus throwing the CEL.

Below are some links to CEG on the matter and should clear up any confusion and give some more insight. BTW, I have removed my DPFE and cleaned it because I go 4 CEL's in a span of 2 weeks, about 2-3 months ago for this same thing. I disconnected the tubes leading to the DPFE and cleaned them out. I then tapped on the sensor housing and watched as a lot of carbon soot fell out. I made the mistake of removing the sensor and trying to manually clean the passages with rubbing alcohol and a Q-tip. DON'T DO THIS! Apparently, the sensor is very sensetive.

CEG Topic: CEL P0401 Insufficient EGR Flow
CEG Topic: PFE Sensor out again in 1.5 yrs.!!!
 
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so could you reroute pipe after the dpfe thing and run it back into the y-pipe like were that test port is then the egr would apear normal up top would function for the computer and would eliminate the exhaust gases in the combustion chambers.
 

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I disconnected the DPFE electronics, and the car ran just fine without any CEL, but I am unsure if my driving parameters warranted EGR activity ... I only took it for a spin with the DPFE disconnected. Only way for me to tell is to unplug once I get the car running again (no battery hookup) and drive it for a few day to see if I get a CEL. I am sure that I will. As for your question, I am sure that you could ... let's just hope that the emissions police don't find out
 
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