# Secondary Air System Assistance



## steckrca (Dec 28, 2006)

Ok so here's the deal. I think I've pretty much got it sorted out (in my head), and I'm looking for some confirmation before I begin delving into this thing. 
2001 A6 4.2, ~97000 miles, bone stock.
The check engine light in the car has been on since I bought the car in February, with 90K on it. I've checked the codes a few times, and each time, it's given me a secondary air system and o2 sensor code. I was told when I bought the car that it was the air pump, but I've been skeptical ever since, so I did some reading today. I've searched a lot, and have found a lot of good information, but none really pertaining to my actual question, so here goes.
The code for the secondary air system reads "Secondary Air System (Bank 1)." This says to me that the pump is good, as it would throw a code for the actual pump if the pump weren't functioning. Or it would throw a code for the pressure being too low, etc. So I'm thinking that the pump is good, just something between the bank 1 cylinder head and the pump is faulty.
The second code for the o2 sensor is also for bank 1, sensor 1. I've read that the secondary air system really only functions on cold starts, is this true? Something about how there's more fuel being delivered during startup, and thus more unburnt fuel in the exhaust, and that's where the air pump comes in. Anyway, both codes coming from the same bank of cylinders tells me that I have a leak in the tubing between the air pump manifold and the cylinder head on bank 1, or perhaps a secondary air system combination valve on bank 1. In short, something between the pump and bank 1 cylinder head.
So quick recap. 
1. Secondary air system failure (bank 1)
2. Oxygen sensor (bank 1)
3. No code thrown for the air injection solenoid valve, assumed good.
4. No sensors on the combination valves, need to be checked.
5. Assumption is that there is a faulty hose or valve on bank 1 after air injection solenoid valve.
Any advice, opinions, or maybe even pictures would be uber stellar. Thanks, sorry for the long post!!


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## Slimjimmn (Apr 8, 2006)

*Re: Secondary Air System Assistance (steckrca)*

Check the combi valve at the back of the cylinder head passenger side (b1) and see if it holds vacuum. Also check for the 1/8" vacuum hoses to see if they are cracked or broken. IMO I would just replace the front o2 sensor on that side because I have done so many. The front o2 sensor reads to see if the sec. air is actually injecting air into the system. Sometimes a failed o2 sensor will give false signal to ecm saying sec. air is not being injected.


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## steckrca (Dec 28, 2006)

*Re: Secondary Air System Assistance (Slimjimmn)*

hey thanks for the reply. i'll obviously check those hoses for leaks, etc. before I change the o2 sensor, but if I don't find anything, I'll go ahead and change it...couldn't hurt. Thanks for the advice!


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## steckrca (Dec 28, 2006)

Well I finally got in there and took a look at things. The vacuum line going to the combination valve on the bank 1 cylinder head was completely off, and the end was all torn up, as vacuum lines do. It had plenty of slack in it, and the rest of the hose looked good, so I just cut the end off, and reattached it. I went immediately to Advance Auto Parts to read the codes, and the o2 sensor code had cleared itself out, but the secondary air system bank 1 code had not. I cleared it out, and it didn't come on during the ride home. I'm pretty confident that it won't come back on since I obviously fixed the o2 sensor code by reattaching the vacuum line. We'll see!


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## steckrca (Dec 28, 2006)

The drive home yesterday with a few stops (never cut the car off) took me about an hour. The CEL didn't come back on within that time. Drove to work today after letting the car warm up for about 10 minutes, about 7 miles, 12 or so minutes, no CEL. Leaving work today 10 hours later, CEL comes back on. Went straight to advance to read the codes, P0130 o2 sensor circuit malfunction bank1, no secondary air system code. I took note of all the freeze frame data when it came on, maybe someone can make sense of the following:
P0130 O2 Sensor Circuit Malfunction
1520 RPM
Load 7.4%
Coolant Temp 203 F
Short Term Fuel Trim1 0%
Long Term Fuel Trim1 0.8%
Short Term Fuel Trim2 1.5%
Long Term Fuel Trim2 0.8%
Short Term Fuel Trim3 -100.6%
Long Term Fuel Trim3 -100.6%
Short Term Fuel Trim4 -100.6%
Long Term Fuel Trim4 -100.6%
Speed 38mph
Fuel System 1 CLSD
Fuel System 2 CLSD
Pretty sure I'm going to have to change that o2 sensor, but I'm still skeptical for some reason. 
Anyone?


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## chockrl (Oct 14, 2009)

I've had similar issues, starting the first cooler day last week. I am not getting O2 sensor codes, but both bank's of secondary air system. Just bought an 2004 S4, 46,000 miles. I'm trying to track down all the vacuum lines, and I hear the pump running on cold startup. The first codes came a couple min. into my drive to work, but after clearing them the last two times they have shown up were towards the end of 10-15min. drives. I've had a hard time finding good info about how the system operates and what would cause it to show the codes after the car is warmed up.


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## steckrca (Dec 28, 2006)

There's a PDF for the diagnosis of the secondary air system for the 4.2 floating around, that might be a good starting place for you. But it's pretty simple anyway, pump to the solenoid in the center rear of the engine, then out to combination valves on the rear of each cylinder head. If you're throwing both bank codes, you've probably got a bad solenoid. I was only throwing the bank 1 code, so I knew the solenoid was good. If you hear the pump, it's probably not that either. I don't remember if the solenoid will throw its own code, it may or may not have its own sensor...


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## Slimjimmn (Apr 8, 2006)

*Re: (steckrca)*

good to see the hose was broken, its common. No vacuum line lasts very long in euro cars because they get so hot under the hood. 
If you still get the o2 sensor code than replace the o2 sensor. They usually last arround 90k miles


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## chockrl (Oct 14, 2009)

Checked the vacuum to the valves this morning in the cold. The solenoid is working, and there is no vacuum leaks. The pump is also running. Any links to that pdf, that is exactly what I have been searching for!


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## Slimjimmn (Apr 8, 2006)

*Re: (chockrl)*

the valves can fail also. You can check them with a vacuum pump, they should hold vacuum.


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## chockrl (Oct 14, 2009)

The valves do hold vacuum. So I had a new theory after checking that all the vacuum lines and solenoids were working. Being new to me, I have been babying the car until it gets to the normal water temp operating range. But instead of that, I have been letting it warm up some, and then driving it harder sooner. For two days I had no check engine lights, until last night coming home from work. Got in a construction zone shortly after leaving work, and before I knew it the check engine was on again. Same codes, P0491 and P0492.
So it seems that both of my o2 sensors are slow to warm up in the high 30's to low 40's temps I've had here the last week or so, but if I heat up the exhaust with the throttle they are fine. Just a theory.


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## chockrl (Oct 14, 2009)

*Re: (chockrl)*

Found the root cause, hopefully, of my fault codes. Broke down and jacked the car up to take a look at the secondary air pump and lines. After tracing the lines I found that the pressure side hose which is near the air box, under the passenger side radiator hose was completely off. Hopefully problem fixed, thanks for all the help.


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