Chevy Vehicles’ Relief Valve May be Sticking
This bulletin applies to 2019 Chevy Express, Silverado and Suburban vehicles, equipped with a 6.0L L96 engine.
A vehicle may have a concern of no oil pressure and/or DTC P0521 set. The relief valve in the oil pump may be sticking, or the number 1 main bearing may be damaged.
Check the engine oil dipstick to confirm that the oil level is not under or overfilled. Confirm oil pressure at the main gallery with a manual gauge.
If pressure is lower than specification, replace the oil filter. If no improvement is found, remove the oil pan and inspect for number 1 main bearing damage.
If the bearings are OK, change the oil pump. According to GM, Chevrolet engineering is currently working on a root cause.