P0411 after changing the MAF - What did I do?

[dirtyguido]

Hey guys,

Swapped the MAF, to fix my "long term fuel trim too lean" CEL and i did disconnect that one hardline that runs to the right of the airbox I did pop it in back in after I was done, was that supposed to pop in and out or did I break something by accident?

The day after the MAF swap I got my first P0411 code. I had these codes randomly on a couple other cars so I read it and cleared it. I drove the car for a week and about 300 miles and all was well, then today I put new wheels on the car, took it for a ride, and 5 min into the drive I get the CEL again, P0411.

So I'm wondering, did I break something, did I loosen something? Where to start?

I need to get the car through NJ inspection by the end of the month, so it's also pretty urgent. The one random thing I noticed was the fact that last time I got gas, the car struggled to start a bit, right after the fillup, I gave it a bit of throttle and it fired right up...

Opinions, Ideas, all help greatly appreciated...

George

[Jman25]

Sounds like a vacuum leak to me, I had that same problem of running lean, my gas millage was crap, and occasionally it would stutter like that. get some brake parts cleaner (non chlorinated kind) and spray it on the connection lines of all the vacuum lines in the engine, if you have a leak the engine will suck that cleaner in and the engine will bog-down big time. My problem ended up being the silicone hose between the intake manifold and the fuel regulator, it was old as hell and had a hole in it. One four inch tube and 2 zip ties and no more problem. Good luck PM if you have any questions, I've become an expert in vacuum leaks given all my problems.

[dirtyguido]

Ok, so if the car didn't have the problem before I pulled the airbox top off to change the maf, and now it does, where should I start looking? I'm a noob when it comes to these audi's... But I have NO problem getting my hands dirty...
Thanks in advance,
George

[Jman25]

look right around those hoses around the air box, I replaced all those one time use clamps with real ones, a few were loose meaning I could move the hose back and forth from where it was supposed to be staying put. there should be a vacuum line diagram on the bottom of your hood possibly like mine. Follow those black hose lines around youre engine bay brake parts cleaner will become your new best friend. It also took some time for my MAF to reset after I cleaned mine so be patient if thats the case. Ill try highlighting a pic of my engine bay to give you and idea of where to look.

[dirtyguido]

Ok that would be great!
As far as the maf, I didn't bother cleaning it but rather I just replaced it with a brand new one from ECS. I cleared that code and the long term fuel trim code is gone and has not returned.

However, since that day, the next morning it threw a p0411 - secondary air injection, incorrect flow direction. I didn't have a p0411 problem before that, so I'm afraid I solved one problem but caused another. I cleared the code the first time, and it took a week and about 300 miles to return.

I agree that there is a probable vaccum leak somewhere, either that or a check valve causing a problem... these cars seem to have one of the most convoluted vaccum setups I have ever seen...

[revolution337]

x2 on the vacuum leak. i had the same code, and i had a couple cracked vacuum lines that i replaced and solved the problem.

[walky_talky20]

The cause for this code is almost always failure of the small vacuum line that goes to the Combi Valve. It usually rips right near the combi valve due to excessive heat exposure over a long time. By moving things around when changing your maf, you may have merely finished off an already damaged hose.

See this photo where the vacuum line has been replaced by a nice red silicone hose:

[dirtyguido]

My engine looks a little bit different than that... The valve is further underneath (I have an ATW motor) How many vac lines does that valve have coming off of it? Mine seems to have one longer one that leaves that valve, and goes between the intake runners to underneath the intake manifold. I just got home so the car is still way too hot to screw around with. This line is plastic hose though, not the braided fabric stuff which leads me to believe it's been replaced. Is there another short line I can't see from the angles I'm looking at?

The braided fabric line between the FPR and the intake manifold seems worn with obvious signs of fraying. The other thing I noticed is this hard plastic pipe that looks like a y of sorts one right next to the airbox, there is a check valve there and a short piece of hose that bends 90 degrees and goes to a hardline directly parallel to the airbox. That's what I popped off and replaced, although there was NO clamp there, BUT there was the impression of a clamp on the hose. (the check valve seems newer so it could be a faulty replacement job). I put a zip tie on that line when I reconnected it... The Other one use clamp has obviously been tampered with and isn't tight anymore, it will litterally spin around the hose....

I'll go take pics in a few... brb...

George

[walky_talky20]

There is only 1 vacuum line that goes to the combi valve. I showed a picture of an AWM engine because it is a bit easier to see. ATW is basically the same, but the valve is tucked down a bit farther.

If the vacuum line looks good up to the valve, you can follow that line to the control solenoid under the intake manifold and then make sure the vacuum source line to the control solenoid is all good. Other than that, check the air piping between the secondary air pump and the combi valve.

[dirtyguido]

Would any other vac leaks potentially cause the problem? Or would it be limited to those things (or a failed combi valve or secondary air pump itself).

Pics coming in a second.

George

[dirtyguido]

Hopefully this all makes sense!

George

[walky_talky20]

Looks like the line to the combi valve has definitely been replaced, it isn't really routed properly.

I would follow that vacuum line to the control solenoid and check the other line coming to that solenoid. I would also check the operation of the combi valve itself by applying vacuum to it to make sure it opens and closes properly. You can do that with your mouth by sucking on the vacuum hose or with a vacuum pump. Also I would check the operation of the secondary air injection pump and control circuits using vag-com "output test" mode. You can take the air line off the combi valve and make sure the pump is pushing air while running the test.

[Jman25]

I would replace that short hose to the FPR and the Throttle Body manifold, that was what I replaced move it around a bit but hosing is so cheap it is worth replacing and definitely get yourself some small clamps for those lines around and for that zip tied one. Hopefully that takes care of your issues.

[dirtyguido]

I will do that, at least as a start...

I've seen all sorts of crazy stuff concerning the Secondary Air system:

1) pump being bad
2) fuse in ECM compartment blown
3) combi valve failed
4) adapter attaching it to the head being gummed up and not allowing air to flow into the head.
5) vac leak to combi valve
6) relay bad
7) solenoid that sends vacuum to combi valve bad
9) line between airbox and pump having pinholes

I did some thinking and realized that maybe the P1128 long term fuel trim too lean code I had due to the bad MAF actually may have been masking this underlying problem.

Basically the point of these EGR, and SAP systems is to pump air into the head to artificially lean out the mixture during a cold start, hence raising EGT's and subsequently warming up the catalytic converters quicker so they reach their operating efficiency.

Now, this whole system only engaged upon a cold start, and runs for a grand total of 100 seconds. Apparently it helps emissions, as my 1.8t is considered a ULEV for the year 2000. Forgoing the discussion on the necessity of the system and it's effect on emissions, it is required and has to be operating properly here in NJ to pass state inspection. All they basically do is plug in and check for no codes, and all readiness monitors ready.

BUT what I started to realize is that the car has no ECU connection to the SAP system to check flow. All the ecu does is tell the SAP system to engage based on some measure of engine temperature. This inadequate flow detected code simply must be a guess by the ecu based on not seeing the leaning out condition it's trying to create based on the pre / post cat 02 sensors.

Since the car had a bad maf when I got it, which manifested itself as a p1128 long term fuel trim too lean code, but the fuel trim was not that bad at idle. So maybe the maf was covering up this SAP fault?

Ok I'll get off my soapbox now...

George

[walky_talky20]

That is a plausible theory. I do believe it measures the SAI effectiveness based on O2 sensor readings. I would think it would watch O2 sensor readings when the SAI kicks in - looking for a change.

You can check a lot of the SAI components using vag-com output test mode. You can kick on the SAI pump to make sure that works, which is also checking the fuse, relay, and wiring at the same time. I believe you can test the SAI control solenoid there as well.

If the vacuum line has already been replaced, given the pump works, you may be looking at a bad or clogged combi valve. It could be the solenoid, but I think those fail much less often.

[dirtyguido]

Current observations:

First I put two real hose clamps on the sides of that check valve by the airbox, then I replaced the vaccum line between the fpr and the intake manifold. The old one was frayed on the outside, and the clamps were meaningless, it just slid off each side with the prod of a flatblade screwdriver. I can't really tell if it was compromised or not, but regardless it was in bad shape.

Then I cold started the car, and let it run for 3 mins at idle. The SAP pump does run, and doesn't sound bad. And it shuts off after the prescribed period of time. That eliminates the pump, relay and fuse. So it's either a vac leak, solenoid, or combi valve, or an air leak in the in or out lines to the SAP from the airbox, or from the SAP to the Combi Valve (assuming these minor vac fixes didn't take care of it).

I scanned the car after that, and there were no codes, but 3 of the monitors are still showing incomplete for readyness. First Sec air, then o2 sensor, then evap. I cleared the code yesterday afternoon and so far no recurring codes, but then again, it prob needs much more of a drive cycle to set all the readyness monitors.

More to come,

George

[dirtyguido]

Well at this point those "fixes" didn't help the situation..

As soon as the car cold started for the 3rd time, despite the fact you hear the sap pump clearly working, it threw the CEL p0411, but it showed secondary air as "ready" in the obd2 monitors....

So the search continues... I'm going to check the pump and the lines going to / from the airbox first, because those were the most likely to have been disturbed unknowingly during the MAF install...

[dirtyguido]

Well I'll be damned.

I cleared the code after it threw it, and then scanned the car again when I came home (yes I can be OCD when it comes to things).

There were no codes, but I noticed something, this time there was only one incomplete readiness monitor, for Sec Air, the Evap, and o2 had become ready for the first time since I got the car. I was onto something...

So I did some searching, and found out that to set readiness for Sec air, the car needs 3 cold starts where the Sec air injection system is engaged, and the car is allowed to idle for 3 mins.

I purposely started the car early this morning, followed the procedure of letting it idle for 3 mins, and shut it down, scanned the car, same results, no codes, sec air incomplete.

Let the car sit for a couple hours, repeated. And low and behold, no codes, all monitors ready. I ran it down to the inspection station at lunch, and it passed obd2 and everything.... So that worry is gone for 2 years!

In the end it appears that the sec air system is very sensitive to even the slightest vacuum leak. Even if it is at a component completely irrelevant to the sec air injection system. My guess with this would be that the combi valve requires a significant amount of vacuum to open properly, and stay open.

So it seems that just adding the 2 clamps to both sides of the check valve on the evap purge valve hose, and at 4" piece of vac hose between the fpr and the intake have solved the problem, at least for now...

Thanks again for all the advice.

George

[walky_talky20]

That's great. It's cool when stuff works right, eh? I bet the drive to the inspection shop was with with your fingers crossed!

[dirtyguido]

Actually In Jersey, they are state run, and look like big warehouses with bay doors, and have an assembly line setup, where the car goes down the line and someone else checks each component at his station...

When I got there there was about a 15 or 20 min wait, and I didn't want to shut the car off because I didn't want it to possibly have another cold start. Cost me a bit of gas, but worked out well.

Despite the worrying, so far no CEL, and I scanned it again, and no codes either...

George

[Seerlah]

I like it when AZ comes together to fix an issue with the most help done by the OP themselves. Good job, man!

[dirtyguido]

Thanks Man

It worked out well, and at least for now the code hasn't come back.

The biggest relief is having the inspection nazi's out of my hair for 2 years! By the time the next inspection comes around, if things go according to plan the car won't be recognizable anyway!