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.

[The_Laird]

Originally Posted by 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.

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

[MikkiJayne]

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.

[The_Laird]

Originally Posted by MikkiJayne

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.

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!

[steamship]

Originally Posted by The_Laird

I couldn't get to the vacuum reservoirs without major (for me) dismantling work.

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_Laird]

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.

[MikkiJayne]

Plastic is standard, but many of them have already been replaced by braided hose, probably multiple times.