We've had a wiring issue with the engine loom at the back of the engine were it goes across to the bulkhead. If you cut the loom open from the inlet manifold, there are three red wires soldered together and this connection fails. I'm not sure exactly what this affects but there is a motorised controller (boost controller?) by the compressor which doesn't operate correctly, allowing less pressure through to the secondary air injection system, which in turn logs this fault code. Low reading MAF sensors can also result in this code.