Sticky relief valve
This TSB applies to a number of GM vehicles, ranging from 2008 to 2013, equipped with any of the following aluminum V8 engines:
L76, L77, L92, L94, L99, L9H, LC9, LH6, LH8, LH9, LMG, LS2, LS3, LS7, LS9, LSA AND LZ1. All share the same type of oil pump pressure relief valve.
Some customers may complain of low or no oil pressure, and/or engine noise, which may be the result of a sticking oil pump pressure relief valve. In some instances, this may occur intermittently if the valve frees up when the engine cools down.
If diagnosis isolates low mechanical oil pressure at the oil filter housing and oil pressure sensor, replace the oil pump, flush the oil cooler lines (if so equipped). If an engine noise is noticed after replacing the oil pump, follow service manual instructions and repair or replace the engine as necessary.
(Yeah, low or no oil pressure can be a bummer.)