Oil Out the Vent

WARNING: This page is about a different car, the 2010 GMC Sierra and 2010 Chevrolet Silverado. However, it is still accessible from the selected car via links, so may be relevant.

Checks	Causes
Input Speed Sensor	ISS loose in bore
ISS O-Ring	Damaged or missing
Oil Pump (4)	Chamber in pump body rotor pocket
Miscellaneous	Fluid level - overfilled