VCDS Fault code
 

My engine warning light came on yesterday and a scan today through up “secondary air injection system (banks 1 and 2) insufficient flow”

Any ideas what this is?

Thanks, Jim

Secondary air is a pump which blows fresh air down the exhaust from a cold start to light off the cats quickly. Its a pointless waste of weight and complexity for an unmeasurably tiny reduction in emissions. If you get in the car and drive it straight away 99% of the time it doesn't even need the secondary air.

This code usually happens because the brittle plastic pipe connecting the solenoid valve on top of the bank 2 fuel rail to the two SAI vacuum valves has perished and broken and so they aren't actuating on a cold start. The ECU can see they're not working by the readings from the secondary O2 sensors.

Its simple enough to fix by replacing the broken plastic pipe with standard 4mm braided vacuum hose and a T piece.

Thanks Michaela. I cleared the code and it’s not come back! I popped it up to my local garage to book a service and he suggested a possible data corruption if it’s been little used in a while. I think that may be possible as the scanner didn’t recognise the car when I plugged it in.

How’s the migraine - better, I hope.

Thats what I mean about it not needing it every time. I threw all that stuff in the bin on my S8 and the error popped up maybe one in ten cold starts until I had it mapped out. The error will only come up in the rare circumstance it wants the system and finds it doesn't work.

No migraine today thank you.

Is it possible to map it out without removing “all that stuff”? I’ve got VCDS

You can't map it out with VCDS - that can only change the coding whereas to permanently remove it the ECU needs to be flashed with new code, the same as a traditional remap.

It can be DIY'ed using Nefmoto software and a generic OBDII to USB cable, but that does carry some risk as it has the potential to brick the ECU if it doesn't work or goes wrong.

The easiest solution is to just fix the vacuum pipes to the solenoid and the two SAI valves so the system works again. There's not really any advantage to mapping it out when you still have all the hardware in place and don't plan to remove it. Its more the remap allows the hardware to all go away.

Thanks Michaela. Do you have a photo of the vacuum pipes so that I can locate them and fix the problem?

Vacuum line schematics are in the engine service manuals in the thread linked below. I've used them myself to rebuild mine. A roll of vacuum hose is £15ish on eBay

http://forum.a8parts.co.uk/showthread.php?t=9345

That was quick -thanks loads! +++

The only pics I could get of this stuff is either in the bin or on the workshop floor :ROFL: Better to go off the manuals +++

Unfortunately, I seem to thick to find the right page in the manuals :(

I can't find them either :(

Well, then there’s no hope for us mere mortals if the D2 Doctor can’t find them :ROFL:

Start from page 30 of the following PDF:

SSP 217 V8-5V Motor Audi.pdf

I think when I did mine, I followed the instructions at the following page:

http://www.audipages.com/Tech_Articl...sereplace.html

... and only replace one section at a time.

Thanks Sean. Is this what I should order to replace the hose?
https://www.ebay.co.uk/itm/COTTON-BR...edirect=mobile

That looks perfect. Admittedly, when I did mine many moons ago, I opted for blue silicone rubber... just to be different.

Well, she's spot on yet again (see photo below). And thanks to Sean as well for sending me the guide from Audipages.com. I only replaced the plastic pipes that Michaela mentioned as I couldn't get to the vacuum reservoirs without major (for me) dismantling work.

Started it up and the engine management light went away without even needing to clear it!

That's the ones that failed for me, right at the back of the engine bay. The rubber pipes had gone brittle and were falling apart, and it was literally the braid holding it together.

The pipes that I photographed were just plastic - not braided rubber (they are now though!). One had snapped. I re-used the T-connector and will replace the rest of the hoses as and when I need to, or when I have more stuff off the front end.

Plastic is standard, but many of them have already been replaced by braided hose, probably multiple times.

The problem persists! Sometimes it will stay clear for 600 miles or more, but the engine light eventually comes back on. IIRC, Mike suggested that the vacuum valves themselves might be blocked and that they can be flushed out with Fairy Liquid and water.

Can this be done in situ, because it looks like a right sod to remove them?

if you're getting a code for both banks, and all the vacuum pipework is good, its unlikely to be the valves. More likely the pump, which is in the airbox. That can seize up from moisture ingress but won't trigger a specific code. There might be an output test for it in VCDS so you could try that and see if you can hear the pump running.

I replaced the plastic pipes at the back of the engine with braided rubber and the warning light and error code (for both banks) disappeared immediately. But then a while later it was back. All the pipes that I can see look fine, but some of them seem to disappear into the depths of the under-bonnet wilderness!

I’ll have a look for an output test on VCDS. Thanks again.