SAI Incorrect Flow.. Stumped

[fR3ZNO]

Been having some issues diagnosing SAI codes (P0411) on my friend's 2.8 C5. It's an ATQ. I've gone through the whole system and I still get an incorrect flow code and "System Not OK" in VCDS for both banks when I run the test in Basic Settings.

I started with replacing the air pump, was full of water that was brown due to rust. Also replaced the hoses going to and from the air pump. Pump will turn on when testing the relay in Output Tests in VCDS. Can feel strong rushing of air with pipe disconnected from air pump. So it's safe to assume that the relay and fuse are fine if it's running during the VCDS test?

Then, I checked the combi valves, both were so caked with carbon that a can of carb/choke cleaner didn't help. Pulled a set from PnP and bench tested them with MityVac hand pump. Held vacuum and valves opened when vacuum was applied. While installing them, I used some gasket paper (made holes and trimmed edges to fit) and a very light coat of RTV to hold it in place when installing on the cylinder heads.

Double checked vacuum line routing, according to the diagram under the hood, everything looked okay to me. Only thing that I noticed was the blue check valve seemed to be backwards. But the check valve did work, could only suck air through on one side. Put that side towards the vacuum source. Also checked to make sure that there was vacuum from line while car was running. Vacuum lines had been previously replaced with silicone line.

With the output tests on VCDS also checked the N112 solenoid valve, could hear solenoid clicking and verified that vacuum could pass through when it was energized.

So, even after all of this when I run the test in Basic Settings (channel 77 for one bank, 78 for the other), it will run and then the result is "System not OK" for both banks. Then fault codes are stored for SAI insufficient flow on both banks. I noticed that while the test is running, MAF % reading while go down to -100%~ or so, VCDS states specification is -100% to 50%. I would imagine that -100% would show that extra air is being sucked from the air box into the combi valves (but not necessarily into the exhaust stream)?

The only thing that I can think of is that the hand made gaskets were installed backwards and is impeding airflow or the passages in the cylinder heads themselves are clogged with carbon. I don't believe the passages are clogged however, since cylinder heads mating surfaces were decked for a head gasket replacement a few months ago. I believe they were hot tanked, so that would remove any carbon buildup in the passages.

I apologize in advance for the wall of text. I'm at my wit's end with this and can't figure it out.

Thanks,
Dave

[a4kamila6]

I have p1423 code on my 2.8 ATQ, says insufficient secondary airflow bank 1 which is passenger head. Changed egr, changed pump, changed solenoid, changed check valve and basically all the vacumm lines, even tried removing egr and seeing if I could get carbon dislodged from the egr passage. No luck. driving with the code for 5 years now almost. Many people have suggested ripping the head off and cleaning it but for my daily driver thats makes no sense at all. got a c5 im invested in.

[PaperToast]

i wouldn't worry about it.
it seems that the ecu is so stinkin' sensitive to this if its off by .00001 lb/min of air, it triggers the code.
you can thank the epa for having audi install this junk.

[fR3ZNO]

I have p1423 code on my 2.8 ATQ, says insufficient secondary airflow bank 1 which is passenger head. Changed egr, changed pump, changed solenoid, changed check valve and basically all the vacumm lines, even tried removing egr and seeing if I could get carbon dislodged from the egr passage. No luck. driving with the code for 5 years now almost. Many people have suggested ripping the head off and cleaning it but for my daily driver thats makes no sense at all. got a c5 im invested in.

I understand the desire to not remove the head and clean it, but like I mentioned it had been removed for head work for a head gasket job. So the passages and everything should be fine after a hot tank cleaning.

i wouldn't worry about it.
it seems that the ecu is so stinkin' sensitive to this if its off by .00001 lb/min of air, it triggers the code.
you can thank the epa for having audi install this junk.

I do want to worry about it. I don't know how emissions and state inspections work in Colorado, but in NY the ECU can't have any fault codes or check engine light on and only one emissions system can fail readiness since its a 2000MY. Now, I can force readiness with VCDS if I'm worried about passing inspection, but my friend wants to sell this A6 and a CEL usually scares off most buyers who aren't VW/Audi savvy.

What I find strange is that I had a B5 2.8 with up to 210k miles before I sold it, and never had an issue with the SAI, who knows maybe someone spent a lot of money fixing the system before I got it. I guess it's hit or miss.

[PaperToast]

I do want to worry about it. I don't know how emissions and state inspections work in Colorado, but in NY the ECU can't have any fault codes or check engine light on and only one emissions system can fail readiness since its a 2000MY. Now, I can force readiness with VCDS if I'm worried about passing inspection, but my friend wants to sell this A6 and a CEL usually scares off most buyers who aren't VW/Audi savvy.

What I find strange is that I had a B5 2.8 with up to 210k miles before I sold it, and never had an issue with the SAI, who knows maybe someone spent a lot of money fixing the system before I got it. I guess it's hit or miss.

i understand that worry. here they can be picky, seems to depend on who you get and which side of the bed they woke up on that day.
but yea, its hit or miss with the sai. i replaced my pump a while back, and it still gave the low flow codes.
i never did figure out what the deal was, i pulled the entire system when i installed 034's silicone spider hose kit

[a4kamila6]

I understand the desire to not remove the head and clean it, but like I mentioned it had been removed for head work for a head gasket job. So the passages and everything should be fine after a hot tank cleaning.



I do want to worry about it. I don't know how emissions and state inspections work in Colorado, but in NY the ECU can't have any fault codes or check engine light on and only one emissions system can fail readiness since its a 2000MY. Now, I can force readiness with VCDS if I'm worried about passing inspection, but my friend wants to sell this A6 and a CEL usually scares off most buyers who aren't VW/Audi savvy.

What I find strange is that I had a B5 2.8 with up to 210k miles before I sold it, and never had an issue with the SAI, who knows maybe someone spent a lot of money fixing the system before I got it. I guess it's hit or miss.

Id say carbon build up is caused mainly by bad oil change intervals and maybe running 87 gas.

[mbagge01]

For those of you that have deleted or modified how the ECU sees the SAI system by an ecu adjustment (like nefmoto) I have read that it is necessary to disconnect the SAI pump from the relay when the program option used is to have the ECU still think it passed it's tests and remain supported, as noted on the S4wiki tune page. Does that mean disconnecting the plug from the pump, or removing the relay, or removing one the wires that goes to the relay?

[Mad Cow]

Just unplug the pump electrical connector, you still need the relay there because there's a separate check for that as well.

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