P0411, hose replaced...bad combi-valve/air pump?

**Airboy** · 01-05-2005, 08:48 AM

The CEL on my 2000 1.8T came on a few weeks ago. Pulled P0411 (Secondary Air Injection Incorrect Upstream Flow Detected ) from the computer. Checked here and found that it could be the vacuum hose, combi-valve($$), and/or the pump($$$).

I replaced the hose, which looked suspect, cleared the code but it came back after a few days. I don't think the pump is coming on any more after a cold start (used to be quite noisy, IIRC). If the pump is not coming on any more, it would mean a dead pump or blown fuse, right?

Some questions:

1) Where is the air pump fuse?
2) If the pump is dead, what are the chances that the combi-valve is dead also?

I will check under the hood once the temperature warms up a bit (been -20C for days). Just preparing myself for the coming assult on my wallet...

Thanks

**Sharky** · 01-05-2005, 08:53 AM

The fuse is in the ECM box, if I remember right. 40 amp.

If the pump is dead, and it is full of water, it is BECAUSE the kombi valve went bad.

The water is condensation formed by hot exhaust backfeeding into the piping down to the pump.

Quickest diagnosis is to pull the hose off at the pump. If water comes out, and it smells exhausty, order a pump and a valve.

**Airboy** · 07-04-2005, 05:52 PM

Finally got around to looking into this air pump problem a few weeks ago. Here is what happened so far:

- When I pulled off the flex hose from the air pump to the Combi-valve (to see of the pump was still pumping air), the hose broke in half. I thought may be the cracked hose was the problem and ordered a replacement.

- With the hose off, the pump was still operational as far as I could tell, pumping away after a cold start. The hose/pump was not wet and didn't smell like exhaust.

- Replaced hose and cleared the CEL. Days went by and the code did not return. Yay, I thought to myself, don't have to buy a $300 pump.

- A few weeks later (today), wife said that CEL is on and when I checked, it was P0411 again (SAI incorrect flow detected)

What happened here? Why did it work for weeks after the hose was replaced? Just a coincidence that some other piece of the system broke after the repair?

Oh, when I was replacing the output hose, I hooked up the Combi-valve side and left the pump side open and then started the engine. Through the open end of the hose I could feel pulses of air/exhaust. Is this normal?

One last thing, what sensor is used to determine that the air flow is incorrect?

EDIT
Took things apart again.
- Unhooked the vacuum hose to the Combi-valve, started up car, felt vacuum at the end of the hose (solenoid is OK?)
- Unhooked output hose of Air pump, hooked up a syringe+silicon hose to Combi-valve. Blew into air pump hose...valve closed. Pull syringe to create vacuum (hopefully enough to open combi-valve), blow into air pump hose...valve is still closed.

Assuming I had enough vacuum with the syringe, looks like a bad Combi-valve stuck closed. Is this a common failure?

Is the Combi-valve difficult to replace?

**Airboy** · 07-05-2005, 04:32 PM

Bump

Is it common for the Kombi-valve to fail into the "closed" position? Ususally read about ones that leak and eventually kill the SAIP. I am not sure if I had enough vacuum to open it with a syringe. Then again, when I had the vacuum hose off and started the engine, the suction at the hose didn't feel like much.

Any other way to check it? Visual inspection after removing it from the engine?

**Passatboy101** · 01-15-2007, 11:03 AM

anyone solve this??

**modifiedA4** · 01-15-2007, 11:24 AM

Originally Posted by Airboy

Visual inspection after removing it from the engine?

i've posted this before, might as well again:

Week of May 1, 2001

Subject Number 1:

A4 1.8T Engine Code ATW

In the event you have an A4 1.8T with engine code ATW with the DTC of 16795 - Secondary Air Injection system, Incorrect flow Detected, a leaking Combination valve could be the problem. A leaking valve causes exhaust gas to enter the secondary air system. The water from exhaust condensation travels through the entire secondary air injection system and if the temperature drops below 0 degrees Celsius the water will freeze. In most cases the water causes the air pump to corrode. Inspecting the combination valve will reveal the problem. If the Intake side of the valve is black, exhaust has entered the secondary air injection system.

**Passatboy101** · 01-15-2007, 01:30 PM

Is the intake side the one coming from the engine, if so that side is clear, the side going to the air box is brown, and the entire pump is full of water.

If i were to use one of those SAIP plugs would i pass the smell test for smog once my cat warms up?

Would it still throw codes if i plug it?

**vewybad** · 01-15-2007, 04:48 PM

Originally Posted by Passatboy101

anyone solve this??

That was my first project this year..what I have learnt from this forum is:
Bad combi valve --> Bad SAIP.

Mine was throwing the same code coupled with the classic whistling noise (My neighbors thought I had an experimental car!)

I changed the combi valve, the SAIP and the connecting hoses (mine crumbled into pieces too - also had to spend a lot of time trying to get the bolts off the rubber mounts), cleared the codes and have been good ever since (last Sep)

Going thru my service papers I noticed that both the combi valve and the SAIP had been replaced once before at around 50 to 60K Miles.

**Fastchevy** · 01-19-2007, 09:12 PM

My car just threw code p0411 is this normally covered under warranty.

**TurboJim** · 01-20-2007, 09:59 AM

Originally Posted by Fastchevy

My car just threw code p0411 is this normally covered under warranty.

Probably not. What year do you have an how many miles?

**modifiedA4** · 01-21-2007, 08:21 AM

Originally Posted by Passatboy101

Is the intake side the one coming from the engine, if so that side is clear, the side going to the air box is brown, and the entire pump is full of water.

the side going to the airbox. so if that has got crap in it, the combi valve is bad.

Originally Posted by Passatboy101

If i were to use one of those SAIP plugs would i pass the smell test for smog once my cat warms up? ?

no, your car has to pass all readiness codes.

Originally Posted by Passatboy101

Would it still throw codes if i plug it?

probably...readiness is based on O2 readings, so if the SAIP isnt injecting air on cold start->codes.

**gusheidisky** · 01-27-2007, 01:54 PM

I have a P0411 code on my '99 2.8L V6. The SAIP whines like a turbine. I'm sure it's louder than it should be, but I don't remember what it used to be like. So I'm sure it has to be replaced.

And I'd guess that at least one of the combi-valves is not working right. Is there a method for testing them without removing them? How can you tell whether they open and close when vacuum is applied and air is blown into the inlet tube? Is it audible? I'd rather not remove one if I know it's working correctly. And I'd rather not buy two if I only need one.

The combi-valves look like they're awkward to replace on the V6, right at the back, very close to the firewall. Any tips?

When you buy the replacements, are they complete with the curved sections that actually bolt to the cylinder heads, or just the upper portions to be bolted on to the original bases? And do they come with new seals, or do you need to order the seals.

From other threads in the forum, it looks like the SAIP is about $230, the combi-valves are about $130 apiece, and the two air pipes (from airbox to SAIP and from SAIP to combi-valves) are about $120. So I'm looking at $610 or more in parts. Does that sound about righht?

Thanks for any comments,

- Roger

**Passatboy101** · 01-27-2007, 02:35 PM

well i just did some searching and you can get a uses SAIP pump on ebay for pretty cheap. I got it all with the combi pump and all hoses for 120 shipped.

And also i believe if you relace the valve really soon you may be able to save the pump. I think.

**Purplezr2** · 01-27-2007, 02:42 PM

I have a pump if anyone is looking for one.

**gusheidisky** · 08-14-2007, 03:30 PM

A really late follow-up, because I only just fixed the P0411 problem. And I'm kicking myself in the butt for not having found it earlier. A professional that had worked on the engine earlier had installed the check valve in the vacuum line backward, so there was no vacuum to the combi valves. I reinstalled it the correct way, and all is well.

Moral of the story: make sure there's vacuum in the line to the solenoid valve, and that on a cold start there's vacuum to the combi valve.

Long story for anyone interested. Fairly early in its life, the Passat (my wife's car) was hit in the front right corner, the shroud over the right-side cam belt was damaged, the belt broke, and several valves got bent. It was almost an insurance write-off, but they wanted it rebuilt. A while later, my wife reported hot oil fumes, so it went back to have the oil leak fixed. Still not right, and she eventually took it back again. A few months after that, I noticed the CEL was on; "yeah, it's been on for a while" came the response. The VW guy decoded it, said it's probably the solenoid valve, none in stock right now but easy to replace. We lived with it a while longer, I got a new solenoid valve, installed it, cleared the codes, but the CEL came back on. Note: I failed to check for vacuum, assuming the VW guy knew his stuff.

I eventually bought a pair of used combi-valves, and compared the noise they made as they opened when vacuum was applied using my hand-held vacuum pump with the ones on the car. Same noise. That's when I finally got smart and tested the vacuum line, and found the mis-installed check valve.

So don't be a dumb a$$ like me, be methodical, don't leap to the wrong conclusion.

- Roger

**theMatrix** · 07-22-2008, 05:34 PM

I am trying to locate the check valve and the solenoid valve(mentioned below) on my 2000 Passat. Can anybody point to me where I can find it...

Thanks

Originally Posted by gusheidisky

A really late follow-up, because I only just fixed the P0411 problem. And I'm kicking myself in the butt for not having found it earlier. A professional that had worked on the engine earlier had installed the check valve in the vacuum line backward, so there was no vacuum to the combi valves. I reinstalled it the correct way, and all is well.

Moral of the story: make sure there's vacuum in the line to the solenoid valve, and that on a cold start there's vacuum to the combi valve.

Long story for anyone interested. Fairly early in its life, the Passat (my wife's car) was hit in the front right corner, the shroud over the right-side cam belt was damaged, the belt broke, and several valves got bent. It was almost an insurance write-off, but they wanted it rebuilt. A while later, my wife reported hot oil fumes, so it went back to have the oil leak fixed. Still not right, and she eventually took it back again. A few months after that, I noticed the CEL was on; "yeah, it's been on for a while" came the response. The VW guy decoded it, said it's probably the solenoid valve, none in stock right now but easy to replace. We lived with it a while longer, I got a new solenoid valve, installed it, cleared the codes, but the CEL came back on. Note: I failed to check for vacuum, assuming the VW guy knew his stuff.

I eventually bought a pair of used combi-valves, and compared the noise they made as they opened when vacuum was applied using my hand-held vacuum pump with the ones on the car. Same noise. That's when I finally got smart and tested the vacuum line, and found the mis-installed check valve.

So don't be a dumb a$$ like me, be methodical, don't leap to the wrong conclusion.

- Roger

**GSO_Passater** · 07-22-2008, 06:20 PM

Engine?

Check valve looks like a lawnmower fuel filter (mine is blue and black) in a vacuum line at the back of the engine. The solenoid has two vacuum hoses, again located in the back of the engine, on top of the intake manifold.

**theMatrix** · 07-23-2008, 06:36 AM

Oh I forgot its a 1.8t, I am sorry...Thanks!

**Chaze*r** · 07-31-2008, 05:26 PM

I'm pulling codes:

2 Faults Found:
16795 - Secondary Air Injection System: Incorrect Flow Detected
P0411 - 35-00 - -
16524 - Oxygen (Lambda) Sensor B1 S2: No Activity
P0140 - 35-00 - -
Readiness: 0000 0000

Does anyone have a picture of the combi valve?

**tankzt** · 06-28-2012, 11:06 PM

Originally Posted by modifiedA4

Inspecting the combination valve will reveal the problem. If the Intake side of the valve is black, exhaust has entered the secondary air injection system.

I think I may have this problem. I have the P0411 CEL. Replaced some vacuum hoses and checked as many as I could. They appear fine. CEL came back on. I just took some pictures of the intake side of my combination valve as well as the other side (small tube). Can you tell me if this looks like a bad valve to you? I performed the tests mentioned in this thread on the combination valve. I blew through it and did not get any air passing through. I sucked air out the small pipe to create vacuum, pinched the line to hold it and blew again. I got air passing through this time. When I released the vacuum I could hear the valve closing and air would not pass through after I released the vacuum. So, the valve appears to be functioning.

I have checked the 40 amp fuse in the ECU box. It looks good.

I also checked the lower hose that connects to the secondary air pump. I pulled it off and there was no water. I connected it back up and started the car cold. I could feel and hear the pump running (sounded normal, not loud). After about 30 seconds to a minute it shut off.

I'm guessing the next culprit would be the N112? It must be working if the SAI pump turns on, right?

I'm at a loss of what to check next.

When I did the work to pull the combi valve out I noticed that the breather pipe that goes above the combi valve had all kinds of crap in it. I included pictures of the breather pipe (it attached to the rubber "Y" fitting on the top, firewall side of the valve cover). Can anyone tell me if that is normal?

IMG_2570.jpg IMG_2572.jpg IMG_2574.jpg IMG_2577.jpg IMG_2581.jpg IMG_2586.jpg

Thanks!

**tankzt** · 07-03-2012, 12:57 PM

Update -

I thought I would post an update. I ended up taking my car to a shop that looked at my SAI system issue. They found that the SAI relay that is located under the ECU was bad. They replaced it and cleared the code. Only time will tell if that was the only issue, but looks good so far. They said the relay passed a preliminary test, but upon further investigation one of the terminals was bad.

**doyles-1.8T** · 07-03-2012, 02:27 PM

Nice. Yeah that seems to be the most common issue and fortunately is a pretty easy/cheap fix. Hopefully they didn't hose you for labor, takes less than 10 mins to reach in there and swap out if you can maneuver through the side-panel where fuses are.

**ImTheDevil** · 07-04-2012, 04:37 AM

Originally Posted by Chaze*r

I'm pulling codes:

2 Faults Found:
16795 - Secondary Air Injection System: Incorrect Flow Detected
P0411 - 35-00 - -
16524 - Oxygen (Lambda) Sensor B1 S2: No Activity
P0140 - 35-00 - -
Readiness: 0000 0000

Does anyone have a picture of the combi valve?

To combine two answers in one post, SAP flow is monitored by the ECU using the readings from the secondary O2 sensors. With these two codes, I'd suspect your passenger side post-cat O2 sensor is bad, since you have a direct code for it, and having no readings from that sensor can trigger the SAP code as well, since no signal from it at cold start means the ECU is essentially seeing no airflow with the pump running.

**Steve in Chicago** · 07-04-2012, 07:11 AM

Originally Posted by doyles-1.8T

Hopefully they didn't hose you for labor as it takes less than 10 minutes to reach in there and swap out if you can maneuver through the side-panel where fuses are.

The SAIP relay isn't under the dash with the rest of the relays. It's in the plastic ECM box in the engine bay, tucked under the drivers side of the windshield. The SAIP fuse is in there too.

**doyles-1.8T** · 07-04-2012, 02:33 PM

Snap. So I guess the 373 relay I can see just behind the fuse box is for something else?

Glad I didn't pull it! Thanks Steve. Found some info on it.

Pics of the area with cover off: P0411 SAIP easy fix
Tips on getting there: P0411, replaced combi and saip, help!

**hubb** · 07-05-2012, 02:55 PM

check valves are half white and half grey there are a few of them located in several spots on and around the back of the engine and on the drivers side under intake. also the solenoid your looking for is also under the intake. follow the vacuum lines.

Originally Posted by theMatrix

I am trying to locate the check valve and the solenoid valve(mentioned below) on my 2000 Passat. Can anybody point to me where I can find it...

Thanks

**FrescoGreen01.5** · 07-05-2012, 05:09 PM

theMatrix

I am trying to locate the check valve and the solenoid valve(mentioned below) on my 2000 Passat. Can anybody point to me where I can find it...

(A 2001.5 1.8T AWM engine is pictured.)
N112 is the SAIP solenoid valve, mounted under the intake manifold where the text is.
N249 is the solenoid valve for the DV, mounted on the same bracket as N112.

There are five check valves; four are near N112--you can see one in the photo, over top of the suction jet pump. The fifth check valve is over behind the air box, also visible in the photo. The coolant tank is lifted up for easy access (only the electrical connector is disconnected).

**Strokendiesel002** · 10-31-2012, 07:16 PM

Does anyone know why the 40amp fuse blows?

**doyles-1.8T** · 10-31-2012, 09:49 PM

Because you touch yourself at night.

**Strokendiesel002** · 11-01-2012, 05:41 AM

Haha, cute. I'm wondering if there has been any correlation between the fuse blowing because of too high a load from the SAIL, which is having problems from a failed COMBI valve.

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