Regulator Valve

WARNING: This page is about a different car, the 2005 Nissan Quest. However, it is still accessible from the selected car via links, so may be relevant.

Visually inspect the components for wear and damage.
Check the regulator valve sliding surface and the regulator spring.

Fig 1: Checking Regulator Valve Sliding Surface & Regulator Spring
Courtesy of NISSAN MOTOR CO., U.S.A.
Coat the regulator valve with engine oil. Check that the regulator valve falls smoothly into the valve hole by its own weight.
If damaged, replace the regulator valve set or the oil pump body as necessary.