1 Fault Code found - Secondary Air Injection System - PO411 - 35 NEED HELP

[Polo GTEye N9]

Hello gentlemen and others,

The wife went Christmas shopping this morning.

The 9N Gti decided to give a Check Engine Light but ran same as usual, which is great.

I got the Vag Com out and scanned, it came up with:

1 Fault Code found
16795 - Secondary Air Injection System - PO411 - 35-00
Incorrect Air Flow Detected
Readiness: 0000 0000

Cleared the codes and restarted with no code.

Any one able to suggest why this code happened and should it reappear what needs to be be done?

Cheers Al

[sambb]

cold start it tomorrow morning - pump running? If yes you might be lucky and just one of the pipes has split. Could be the valve too. But if pump not running could be relay or pump itself. let us know.

[h100vw]

Bad pump Al. ket me know if it comes back. I'll sort it out for you.

Gavin

[Polo GTEye N9]

Bad pump Al. ket me know if it comes back. I'll sort it out for you.

Gavin

Thanks Gav and Sam.

I will see what happens in due course!

Happy Christmas and New Year to all!

Cheers Al

[Polo GTEye N9]

cold start it tomorrow morning - pump running? If yes you might be lucky and just one of the pipes has split. Could be the valve too. But if pump not running could be relay or pump itself. let us know.

Hi Sam and Gav,
Cold started it next morning and no CEL. And the same CEL reappeared again this morning. Scanned and reset.

I actually do not hear anything much, have profound hearing loss.

I could get my wife to listen for pump running. Has it got two flexible tubes. One is filtered to atmosphere.

That is if I knew exactly where the pump is? I guess the pump is the thing attached to the cylinder head in close proximity to the battery?

On this Christmas eve, I wish you a blessed Christmas and a great 2018.
Cheers Al

[sambb]

yep follow both convoluted black tubes and they'll lead to the pump. Its between the radiator and the engine tucked in under the inlet manifold. Has to be a cold morning start to guarantee that itll run.

[Polo GTEye N9]

yep follow both convoluted black tubes and they'll lead to the pump. Its between the radiator and the engine tucked in under the inlet manifold. Has to be a cold morning start to guarantee that itll run.

G'day Sam, Thanks for the quick reply.

Okay allow to go cold over night and start then the wife listens for Air Pump to run.

I assume that after warm up Secondary Air Pump ceases to run? Does it run always at cold and what is the normal duration?

So is the CEL an inconvenience rather than an essential immediate service item?

Cheers Al

[simon k]

The secondary air system blows air in behind the exhaust valve
for 100 seconds during a cold start (+5 °C ... +33 °C coolant temperature).
This produces an oxygen rich exhaust gas, causing
afterburning and reducing the heat-up phase of the catalytic converter.

I can't figure out *where* it actually blows the air to get it to go behind the exhaust valve though, doesn't make a lot of sense...

[Polo GTEye N9]

I can't figure out *where* it actually blows the air to get it to go behind the exhaust valve though, doesn't make a lot of sense...

Hi simon k, exactly......... magic?

[simon k]

Hi simon k, exactly......... magic?

it's weird as all f*ck - someone must get it... as far as I know, the pump sucks air in through pipe (8 ), and pressurises hose (9) into the combi valve - sure, makes sense, OK, where does the combi valve send the air to?

well, apply a little bit of vacuum (+'ve or -'ve - one way or the other) to the combi valve through N112 to open the combi valve - that must mean the air gets out via the bottom of the combi at seal (3), right? but if you read all of the stuff about getting rid of the SAI, it says water comes out when you take that off, WTF??

[simon k]

being from a world of Minis though, it does make sense, at least in the "hey, let's reduce emissions by diluting the exhaust with clean air, it's not cheating at all because the exhaust gas analyser says so" world of WTF'ness


from '76 they had a thing we call the "smog pump", the head has a fitting in the front for each exhaust valve chamber and a pipe that connects them to a fanbelt driven air pump - it just pumps clean air into the exhaust - apparently to "promote the burning of any raw fuel in the exhaust", but we know the truth on that one - if it ain't gonna burn at 2000° in the chamber, it ain't gonna burn in the exhaust...

[sambb]

filtered air goes to the pump, is pumped out to the top of the combi tower. When the solenoid atop the cam cover gets its signal (eg cold start) it will activate allowing plenum vacuum to suck the combi valve open. The SAI pumped air then flows through this combi valve, down the stack and takes a right angle turn at the base of the stack. From what I understand there's a long horizontal port that links all the exhaust ports. The pump will artificially lean out the mixture prior to the cat. The o2 sensor will see this lean air at start up and this way knows that the pump is running. If you get the CEL its because the ECU knows its running the pump but isn't seeing the desired effect. The aim of the lean mixture is to turn the cat converter into a fan forced furnace and bring it up to operating temperature asap so that precious seconds of potential climate saving cat converting aren't wasted. It should run for about 20 seconds from memory. Basically the engine can run as rich as it needs to or run what timing it needs to (mixtures etc that may not be favourable to the cat) to get a nice clean start and idle, whithout the exhaust gases being too noxious.

[Polo GTEye N9]

Bad pump Al. ket me know if it comes back. I'll sort it out for you.

Gavin

I have to confess Gav, that about a month ago, Sue had been telling me about a new high pitched noise coming for the direction of the SAI. Yes i could not hear it and Sue said it was there at cold start only and went away after a minute so I ignored it. Until the recent CEL.

Gav, what do you suggest is best practice solution to sort hmm, 'fix' the SAI issue?

Cheers Al

[simon k]

The SAI pumped air then flows through this combi valve, down the stack and takes a right angle turn at the base of the stack.

see, that's what I expected, so why do people talk about losing water when taking the combi off? where does it come from?

[h100vw]

Two choice Al, replace the pump and probably the combi valve too. Or get a tune to fix it. If you're stage 2, I forget, then it's easy for me to arrange that.