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.
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