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Duramax Second Generation: 2004.5-2005 (LLY) Discuss the second generation (2004.5-2005 LLY) of the 6.6L Duramax diesel engine & associated components. 2006 LLY engine discussion belongs in Third Generation forum due to the differences of the 2006 LLY and the 2004.5-2005 LLY. Engine related discussion ONLY.

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Old 03-04-2020, 10:08 PM   #1 (permalink)
kolnerspieler
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04 Duramax P0404 Code EGR issues

Hello,

I am hoping that someone can help me with this EGR issue. The scanner gives out code P0404, and states EGR flow CKT RNG perform.

I started with taking out the EGR cooler and soaked it for days in purple industrial cleaner and it looked spotless once I took it out. Now there is still a chance that it might be clogged, but I would rule that out for now. I replaced the EGR valve and also replaced the MAF sensor, checked the vacuum lines going to the valve, but everything appears to be ok.

What I am trying to understand is how the truck knows when there is an EGR issue? Is there a sensor measuring the flow, or air temperature, or is the truck sensing flow issues with NOx sensors in the exhaust? Does anyone know?

Any other thoughts or places to look for the problem?

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Old 03-04-2020, 10:22 PM   #2 (permalink)
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Old 03-05-2020, 07:04 AM   #3 (permalink)
Rvn4me
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Quote:
Originally Posted by kolnerspieler View Post
What I am trying to understand is how the truck knows when there is an EGR issue? Is there a sensor measuring the flow, or air temperature, or is the truck sensing flow issues with NOx sensors in the exhaust? Does anyone know?
P0404
Modules: ECM
Description: Exhaust Gas Recirculation (EGR) Open Position Performance

P0404 has nothing todo with your EGR cooler.

If the PCM determines that the valve should be operating, but the feedback circuit shows that the valve is not open, this code will set. Or if the PCM determines the valve should be closed but the feedback signal indicates that the valve is open, this code will set.

Possible Solutions:
1. 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.
2. 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.
3. 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.
4. 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.
5. If the voltage doesn't increase incrementally, then repair open or short in EGR control circuit.

P0404 does not necessarily mean your EGR is stuck open. It simply means that the EGR valve is not behaving correctly when the ECM calls for it to be open. These measurements are determined by the MAF sensor, Baro sensor. The valve is not working right, you can get the P0404

I would just replace your EGR valve.
GM Part :97303761 $178.79

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Old 03-05-2020, 08:27 AM   #4 (permalink)
kolnerspieler
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Thank you for the description. So year is 2004 and I have an LLY engine, but mine must have been a very early LLY because I have a vacuum operated EGR valve and not an electronically controlled EGR valve.
I will check on my scan tool is there is a way to activate the EGR valve and see if I can see it move or not. Now that everything is assembled, I probably will not be able to tell anything, but I will poke around on the scan tool to see if there is anything.

So the MAF sensor can tell if the EGR is open? I replaced the MAF sensor as well.

So technically, there is the cooler, the EGR valve, the MAF sensor and that is about it when it comes to components in question.
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Old 03-05-2020, 12:07 PM   #5 (permalink)
firsthere
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Maybe a simpleton idea,
what about an EGR block plate and finger stick to by pass the problem? $50 on Ebay
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Old 03-05-2020, 09:53 PM   #6 (permalink)
jake111
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You have a vacuum pump? Like they had on the EGR'd LB7's? If so, are you sure you have an LLY?

If you have the LB7 style EGR (i.e., with a vacuum pump) I don't think there is an easy way to block off the EGR and the Finger stick doesn't apply.
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Old 03-05-2020, 10:20 PM   #7 (permalink)
kolnerspieler
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I am 99 percent sure that it is an LLY engine. I have the original sticker at my dads house and will take a look just to make sure. I know when my dad purchased it, it was one of the first LLY models at the dealer, so I am not sure if the early models still have the vacuum set up. The EGR valve that I replaced was vacuum operated.
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Old 03-06-2020, 06:55 AM   #8 (permalink)
Rvn4me
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Quote:
Originally Posted by kolnerspieler View Post
I am 99 percent sure that it is an LLY
Look at your vin #
If the 8th digit of your VIN number is a 1, then it is a LB7 Duramax (the early engine). If the 8th digit is a 2, then it is a LLY.
In mid 2004, GM switched to this newer LLY engine.
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