Is that the Secondary Air Pump I'm hearing after start up?

[SlickFix]

On the 3.0 Avant, I've recently started hearing a noise like a fan going in the front of the motor upon start up. Is this the secondary air pump? Is it supposed to come up at every cold start? It does stop after 30 seconds or so.

The reason for my concern is that we've owned the car for two years, and only recently recall hearing it.

If it is malfunctioning or is only running intermittently, could that be the reason for my P0421 and P0431 codes, which currently point to my cats being bad?

[CyberPMG]

The SAI will throw codes of it's own if it is not operating properly. If the SAI is bad, you'll get a code for incorrect air flow (P0411). It will also start sounding like a loud leaf blower. It will eventually throw a CEL. The purpose of the SAI is to warm up the cats on cold startup in order to reduce emissions.

[SlickFix]

The SAI will throw codes of it's own if it is not operating properly. If the SAI is bad, you'll get a code for incorrect air flow (P0411). It will also start sounding like a loud leaf blower. It will eventually throw a CEL. The purpose of the SAI is to warm up the cats on cold startup in order to reduce emissions.

It does kinda sound like a loud leaf blower. Is it very quiet when it runs normally? I'll have to check my codes again, as the CEL is normally always on with my cat codes.

[MacFady]

I'm not sure you always get a CEL with a bad SAI pump but I could be wrong. Mine is definitely bad, I have no CEL. Maybe it's "functioning" properly but it is definitely blowing leaves as well.

[SlickFix]

Any thoughts about going the OEM route vs. much cheaper third-party brand SAI pumps? The OEM Audi pump is something like $679 on ECS, whereas the others are in the $200 range.

[fR3ZNO]

A friend of mine with a B5 1.8T also has the "jet engine taking off" noise from his secondary air pump. When I scanned it for codes it had a SAI incorrect flow and a cat inefficiency code. When his air pump first started to make the noise it only had a code for the SAI incorrect flow, so I'm not sure if the bad air pump caused an inefficiency code as well. He hasn't installed the URO brand pump he bought yet but I'm curious if it will turn off both CELs.

[CyberPMG]

I've been going through a lot with the SAI for my 1.8T. I've replaced it twice with used SAI pumps. First one lasted about 2-3 years. Second one only lasted a few months. Bought a new aftermarket SAI. Still sounds loud and I'm still getting codes. For me, it's likely the combi valve has gone bad which will allow moisture from the exhaust to get into the SAI and destroy it. Since the SAI is under warranty, it's getting replaced, but I'm also replacing the combi valve. Will know later this week if it's back to normal and operating quietly.

[SlickFix]

so I'm not sure if the bad air pump caused an inefficiency code as well.

This really gets to the crux of my thinking. Can a bad SAI pump in turn cause the P0421 and P0431 inefficiency codes. That would really make my day if replacing the SAI pump resolved all my cat codes, too. Of course, there's a hose leading from the SAI pump to the air cleaner box which could be bad, too.

[fR3ZNO]

This really gets to the crux of my thinking. Can a bad SAI pump in turn cause the P0421 and P0431 inefficiency codes. That would really make my day if replacing the SAI pump resolved all my cat codes, too. Of course, there's a hose leading from the SAI pump to the air cleaner box which could be bad, too.

Yeah, that's what I was wondering as well. If left long enough would it cause an inefficiency code? A bad air pump would cause the cats to take longer to warm up which might cause the ECU to think the cats are on their way out. My friend with the 1.8T has a broken SAI hose that goes to the air box as well as the bad SAI pump. We've tried taping it a few times with no luck.

[DJMurphy]

If you can hear the SAI pump operating it's more likely that the hose has just come off the outlet of the pump itself. It's a PITA to reach but on mine I could get to it through the fog light opening.

[evo_ski]

I have purchased used ones and have about a year and a half (45K miles) on my last pump that I snagged off ebay for like $40.

If it is blown and you pull your pump off and it is filled with water your combi valve is bad and needs to be changed.

[SlickFix]

Thanks guys, I'll check the hose and the pump as well.

Regarding the combi valve, the 3.0 has two of them, one on each side. If I pull the SAI pump off and it's filled with water, does that mean I replace both combi valves?

[imnuts]

When I heard my SAI pump, I had 2-3 codes related to SAI, I believe low flow bank 1 and bank 2. Hose on the outlet of the pump came off, so it was blowing no where. I also had codes for both cats being bad. When I reattached the hose and cleared the codes, the cat codes disappeared as well, but they did eventually come back, just took longer than usual. If you can hear the pump, odds are, the hose just broke or came off.

[n7plus1]

rip that shit out haha

[SlickFix]

When I heard my SAI pump, I had 2-3 codes related to SAI, I believe low flow bank 1 and bank 2. Hose on the outlet of the pump came off, so it was blowing no where. I also had codes for both cats being bad. When I reattached the hose and cleared the codes, the cat codes disappeared as well, but they did eventually come back, just took longer than usual. If you can hear the pump, odds are, the hose just broke or came off.

Oh drat, I was afraid that's what you were going to tell me. I'm still looking for the magic cure for the failing cats, short of replacement(and no, I won't go with the catless system & tune).

[fR3ZNO]

Have you considered use spacers on the rear O2s to trick the ECU into thinking the cats are good?

[SlickFix]

Have you considered use spacers on the rear O2s to trick the ECU into thinking the cats are good?

Yeah, I have. But that is not 100% guaranteed to work, and ultimately the cats can get plugged and will have to be replaced anyway.

[fR3ZNO]

Yeah, I have. But that is not 100% guaranteed to work, and ultimately the cats can get plugged and will have to be replaced anyway.

Eh, true. In my case I just can't justify spending 3k$ on cats for my car which is probably worth about 3k if that. I'm almost 100% sure mine aren't plugged they're just getting tired after 200,000 miles.

[SlickFix]

If you can hear the SAI pump operating it's more likely that the hose has just come off the outlet of the pump itself.

Well, well, very interesting. I found that the hose was disconnected on the air filter box, not the pump. So we'll see if reconnecting that fixes the noise. No codes for the SAI, either.

[RDA990]

Any chance you can get a video or audio of it? Mine does start up for 30-1min on a cold start up, but I'm not sure how loud is "too loud" to the point that it isn't working anymore or about to die.

[SlickFix]

Any chance you can get a video or audio of it? Mine does start up for 30-1min on a cold start up, but I'm not sure how loud is "too loud" to the point that it isn't working anymore or about to die.

When it's working correctly it must be fairly quiet, because I never heard it before a couple of weeks ago. Too be honest mine didn't sound as loud as a leaf blower, but it was definitely loud enough to think "What the hell is that?".

[n7plus1]

IIRC, the SAI ONLY runs for that first minute or so of turning the engine over and thats it.

[CyberPMG]

On a cold start, I've had mine run for about a minute. After driving for another minute or two, and I'll notice that it comes on briefly and shuts off again.