P0406 wont go away

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Dcon

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Aug 28, 2019
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My 2003 California egr :( LB7 recently threw this P0406 code. "EGR sensor A high". My vacuum pump is operating fine. I replaced the EGR valve and cleaned the cooler. It wasnt that dirty, and the original one still worked. The code came back. Today I replaced the two Baro sensors. I immediately got 2 new codes, P0238 and P2229 telling me the "new" Rock auto sensors are the wrong ones or junk, or both. put the original Baros back in and I am back to the P0406. I have low power and can only generate 12-15 pounds of boost under WOT. Currently there is stock programming and stock exhaust back on the truck to get it smogged. Truck has 190k, with new injectors at about 160k. I am at a loss with this one. I see alot of info about the P0404, but not much with this. Is there another sensor im missing? Thanks for any input!
 
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Ron Nielson

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Oct 11, 2009
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Assuming you are trying to solve the P0406, So that is a wiring circuit code. Check the wiring and connector at the EGR bypass and see if any problem there.
 
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Dcon

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Aug 28, 2019
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I am still having issues with this P0406 code on my 2003 CA EGR LB7. Would the EGR Vacuum vent valve, 94459951, have issues? There are 2 of them, one has the little filter can broken off. Any idea how to test them? Everything else seems fine and replaced the EGR vent regulator (1997254, 214-636), vacuum pump works, new egr valve, cleaned cooler. I hate to throw parts at it, but i gotta smog this thing! Thanks!
 

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  • LB7 EGR Vaccum Vent Valve 1-700x700.jpg
    LB7 EGR Vaccum Vent Valve 1-700x700.jpg
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Dirttrackdawg

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Sep 28, 2022
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I have the same problem after replacing the MAP sensor that is behind all the egr sensors and valves. This only happens at startup, I can clear the code with the truck running and it will not come back on till the truck is shut off for a bit. My truck is a 2002 California truck LB7.
 
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Ron Nielson

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I have no specific knowledge about that part (vacuum chamber I think), but if something is broken off, I'd replace it. I know they're fairly expensive, but not as much as a diag at the dealer.
 
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Dcon

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Thanks for the replies. Going to replace that Vacuum vent valve and see if that was it. Ron is right, it should be replaced anyway. Dirt track, did you have the P0406, or P0404? Did replacing the MAP fix it? I saw on one of the forums a write-up of a detailed explanation of the the LB7 egr system. Cant for the life of me find it again.
 
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Dirttrackdawg

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Sep 28, 2022
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I had the p0406. I haven't looked into it because the radiator started leaking and I am fixing that first. It's been a bad month for my truck.
 
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Dcon

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Ok. Spent some time on diagnosing this afternoon. Discovered there are actually 3 baro sensors on this CA EGR LB7. The one I didnt notice before is underneath the EGR solenoids and vent valve tee'ed into the vacuum line on the Passenger side. There is one mid engine plumbed into the intake, and the third is drivers side under the large coolant pipe open to atmosphere. The drivers side and passenger side have the same part number, the one into the intake is different. I swapped the passenger side and drivers side. The P0406 MIL went away after clearing codes, and was no longer a pending code either. I now have a pending P2229 Barometric pressure code, but it has not set yet to turn on the MIL light. Probably will as I drive it more, but I think I found the problem and ordered a genuine GM sensor. Not out of the woods yet, but probably on the right track.

Here are the part numbers:
(2) Driver/ passenger side: oem 09350899 ACDelco 213-1155; replaced in 2012 with 12615136
(1) mid engine in intake: 12215049; replaced in 2011 with 12623671

I hope this is it and helps out the next guy. California sucks!
 
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Ron Nielson

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The attachment is the only thing I can find in LB7 Wiring diagrams. I don't understand the squiggly line inside the 3 vents/valves lower right side of diagram. Maybe that's how they indicate a solenoid (or other devices). But there is A side and a B side.
 

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2004LB7

2004LB7

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Ron Nielson said:
The attachment is the only thing I can find in LB7 Wiring diagrams. I don't understand the squiggly line inside the 3 vents/valves lower right side of diagram. Maybe that's how they indicate a solenoid (or other devices). But there is A side and a B side.
Click to expand...
that's the symbol for an inductor / coil of wire. in this case it is a solenoid coil
 
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Dirttrackdawg

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Replacing the sensor caused my P0406. After reading the links above the sensor I put in isn't the right one. I am not sure what Chevy sold me. The truck was looked up by vin. Does anyone know if there is a MAP sensor on the intake in the valley or just the boost sensor on the elbow with the heater and egr butterfly valve?
 
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Dcon

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Just wanted to update. This was the problem. The Baro sensor was the problem. Got it to pass smog a couple of weeks ago, all is good. Now it is going back on the lift to make it gooder :) for another 2 years.
 
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