Are you sure that is a 'sensor'?

It almost looks to me to be the loopback for the blow-off valve.

When under boost, if the throttle is suddenly lifted, the throttle-valve closes and the turbo is suddenly 'pushing' against a closed valve. The sudden spike in pressure is detrimental to the compressor.

The 'loopback' provides a way for this pressure to be routed back to the INLET of the compressor. This helps maintain boost-pressure, is quieter than bleeding to atmosphere and has other benefits.

Think of a vacuum-cleaner when you put your hand over the end of the hose. (only in reverse) The RPMs of the motor goes sky-high.

A turbocharger ALREADY spins upwards of 30,000 RPM... you DO NOT want your turbocharger to suddenly spin up to 50,000+ RPM. (It would likely fly apart like a hand-grenade)

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One 'upgrade' tuners do is to replace this with a valve which bleeds the pressure into the atmosphere. (instead of looping it back) Every time you lift the throttle you get a characteristic "wwwoooossshhhh" sound that the kids love to hear....but also 'wastes' the pressure created by the compressor.

 

It almost looks to me to be the loopback for the blow-off valve.

That is the chunky line underneath it.

That looks to be the "diagnostic" connector for tubing related to the PVC system. It's related to emission control requirements, and will trigger a P1491 when disconnected. (Search the forum for that code.)

Great information. Thanks. I Inadvertently learned a lot about the PCV system now.

 

That looks to be the "diagnostic" connector for tubing related to the PVC system. It's related to emission control requirements, and will trigger a P1491 when disconnected. (Search the forum for that code.)

There's photos of the same connector in 2005 OBXT This thing WTF is it!?!?!? | Subaru Outback Forums and its similar use in a non-turbo in What is this hose? | Subaru Outback Forums .