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 +++