VCDS Fault code

[The_Laird]

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

[MikkiJayne]

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.

[The_Laird]

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.

[MikkiJayne]

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.