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About a month ago my check engine light came on while driving. I stopped several times before I got home and somewhere along the way it reset. About two weeks ago I got another CEL first thing in the morning on my way to work, again it reset after sitting. This week it popped again and stayed on. I got a P0404 and reset it with the reader. That lasted a couple day and it's back on again. I can't find anything specific to GM, only a generic code, Exhaust Gas Recirculation Circuit Range/Performance. Bad EGR? Truck is an 03, all stock, and is running fine.
 

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This is what I read in the service manual: P0404 sets when the ECM detects a lower than expected EGR vacuum sensor signal and a higher than expected MAF rate for more than 8 seconds.

There are many things that can cause this, but you can look for a vacuum leak. In order to properly test the system, you need a Tech II type scan tool, but there are some things you can check with a vacuum pump-gauge. Here are some things you can do:

1:Visually inspect for cracked, broken, loose, or restricted vacuum lines.
2:Check vacuum pump by disconnecting the vacuum line and connecting a vacuum gage- and start engine: vacuum should be at least 15 in Hg
3:Connect a hand held vacuum pump to the following items: each item should hold 15 in Hg for at least 30 seconds.
EGR valve vacuum diaphragm:
EGR throttle valve vacuum diaphragm:
EGR valve control solenoid:
EGR throttle valve control solenoid:

If you do not have a handheld vacuum pump-gauge, you should be able to get 1 at Autozone using their loaner tool program.
 

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unfortunately I'm a bit far from my toolbox and need a large torx head to get that plastic hat off to remove the intake tube. It doesn't seem like I'm loosing any power. Should I just leave this until I get home or am I running the risk of being stranded on the side of the road?
 

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I beleive the plastic hat has a rubber gromet holding it to the torx bolt, just give it a tug and it should come off, dont forget to loosen the hose clamp on the other end.
 

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I am having same problem in my 03 LB7...When I took mine to dealership, they said the EGR was perfectly fine, but it was the new fuel thats messing me up....Apparently when they went to the new ultra low sulfer diesel fuel, it is causing our rigs to run lousy...He said I would have to buy this additive the stealerships sell now to put in to fule tank everytime I fill up to eliminate this problem...Anyone else hear of this?
 

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Leave it till you get home, I have had that light for 9 months, still trying to find the problem.

236ek,
THANKS for those items to look at, it gives me something to try, I will post if I find something........
 

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Rebel,

when I come that way, I will pm for a phone number so we can get together and see if we can come up with something to try to figure this out.
 

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well, it better be soon b/c I am deploying to Baghdad Iraq early next month. I will be gone for 4 months. My wife will be driving it for me while I am gone, so I wanna make sure I get this fixed or not have to worry about it breaking down on her and the kids while I am deployed...I really cant tell it running any different when the light is on or off. Of course, I have only had this truck a few weeks, so I really dont have any comparison.
 

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Yea it does not seem to run different, but if you mash the go pedal, does it stumble?

Mine seems to run fine except when I want to really GO! I have an imminent run coming against a Cummings and I want to be ready, so I want it to go one way, him losing.
 

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No I cant tell it stumbles really......I have noticed though alot of the times the stupid light comes on is when I let it idle for a min.
 

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That is what mine is doing, try putting your foot on the go pedal, and just raise the rpms like maybe 50 rpm, not really noticable, but it will keep the light off. and it only does it warm, when it is cold, it will idle all day with no light until you drive it.

Give that a try and see if it keeps the light off. I can drive my truck for a month with no light, but my wife drives it 10 min. and the light will come on, cause she will idle it at a stop light and it comes on.

I will give ya a call later and we can discuss it more.
 

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Question to the Neens or anyone else willing to let me know if you do....

Will a ECM off of a truck that did not have the EGR stuff work on our trucks?

IE, if we were to just swap the ecm out, will it make this go away and still run?
 
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