P0404 EGR flow issue.

[03Alerosil]

I got a P0404 code. 2003 Alero 3.4. I am almost sure its the EGR valve itself being its a flow issue Any other thoughts on this? Anything I should check?

[sleepyalero]

Usually this code points to either carbon buildup or a bad EGR valve. However that doesn't rule out the following: Open or short in the 5 Volt reference circuit Open or short in the ground circuit Open or short in the PCM controlled voltage circuit Bad PCM (less likely)



Possible solutions...

Using a scan tool command the EGR valve to open while watching the actual EGR position (it will probably be labeled "desired EGR" or something similar). The actual EGR position should be very close to the "desired" EGR position. If it is, then the problem is likely intermittent. It may have been a lodged piece of carbon that has since dislodged, or it could be a bad EGR valve winding that intermittently opens or shorts as the valve temperature changes.

If the EGR "desired" position is not close to the "actual" position, then unplug the EGR sensor. Check for a good 5 Volt reference voltage to the connector. If it doesn't show a reference voltage, repair an open or short in the 5 Volt reference circuit.

If there is a 5 volt reference voltage, activate the EGR with the scanner, monitor the EGR ground circuit with a DVOM (Digital Volt/Ohm meter). It should indicate a good ground. If it doesn't then repair the ground circuit.

If there is a good ground, then check the control circuit. It should indicate voltage that varies according to the percentage that the EGR is open. As it's open more, the voltage should increase accordingly. If it does, then replace the EGR valve.

If the voltage doesn't increase incrementally, then repair open or short in EGR control circuit.

[03Alerosil]

Thanks sleepy. I will find a diagram of the EGR connector and check the wiring. No access to a scan tool but I can watch the voltages as I have a fluke meter.

If the wiring checks out and it's just clogged passages what is the best way to clean them and/or the egr valve? Oh I should add that my Alero has 150k on it.

[sleepyalero]

I pulled all that ogg a google search.


Brake cleaner will be fine to use to clean it.

[03Alerosil]

Getting a new valve today from napa. Going to spray some carb cleaner down the pipe to the exhaust manifold and spray some into the intake. I got some small bristle brushes that should help clean the intake.

Getting a new valve because in my mind if I am going through the work to take it off I am not putting the old, questionable one back on. Plus it's got 150,000 on it.

[03Alerosil]

Put the new valve on and cleaned the port into the intake. Gets rpm much better than before and accelerates like it's supposed too. Big difference.

[sleepyalero]

Good to hear.

[03Alerosil]

The egr valve itself was ok. The sensor controlling it went bad

[sleepyalero]

Easy fix !

[03Alerosil]

It was. The egr valve is very easy to change especially being I have done the LIMG on my car and bolts were already anti seized. The bolt holding the pipe to it was a little hard to break loose

[sleepyalero]

Yeah. I removed mine. One leas thing to worry about haha.

[03Alerosil]

I would of if I could afford the computer tune. Hard to believe that stupid emissions valve caused me so much issues. Kept me from coming to the event over the weekend.

[sleepyalero]

I could have tuned it out haha.

[03Alerosil]

Well shit lol.

[sleepyalero]

How much was the EGR canister? If i remember right they are pricey...

It would have costed you 100$ for me to delete the code on your car.

[sleepyalero]

On autozone app i see 72-83$ for the canister itself. Yeah. Kinda glad i removed that thing haha.


Jesus the tube itself is 76$!

[03Alerosil]

The tube is ridiculous. I paid $73 from o'reilly for the EGR. I reused my old tube, It's just a flexible metal tube. New valve has made a world of difference with my car though. 148,000 miles and still going strong.

[sleepyalero]

Yeah, rarely the tube will get a hole in it.