yes 12 psi the intake manifold sensor is set to 12.5 psi. 15 psi is a boost spike
your can read about it here in cobalt forum
The blower is not maxed out (in termes of rotaion speed) at 12psi, and yes GM did limit the boost pressure at 12psi. The blower will continue to produce more boost pressure until it reaches 12psi, then If the blower rotates any faster and produces a boost pressure over 12psi it will be bled off by the bipass valve so that the engine never sees a boost pressure beyond 12psi.
http://cobaltss.net/forums/showthread.php?t=1085
or here
http://motortrend.com/roadtests/coupe/112_0502_first_cobalt/
oh found this on the cobalt specs page
2.0L ECOTEC Supercharged Engine
The all-aluminum dual overhead cam, 2.0L ECOTEC Supercharged four-cylinder engine is built off the strengths of the original, naturally aspirated 2.2L ECOTEC engine.
The 2.0L Supercharged engine has a four-valve cylinder head, maintenance-free chain-driven camshafts, counter-rotating balance shafts and an integrated oil cooler.
The Eaton M62 supercharger spins at a low rpm, which improves durability and creates less noise while allowing for plenty of top-end power. Power delivery of the supercharged engine is instantaneous. Maximum boost of the supercharger is 12 psi.
Also included on this engine:
A direct-mount oil cooler.
Oil jets for piston cooling.
Heavy-duty pistons.
Strong connecting rods.
Forged-steel crankshaft.
Large oil pump.
Sodium-filled exhaust valves for improved durability.
A high-strength aluminum cylinder head.