1. Check Exhaust Gas Leak

WARNING: This page is about a different car, the 2004 Nissan Maxima. However, it is still accessible from the selected car via links, so may be relevant.

Start engine and run it at idle.
Listen for an exhaust gas leak before three way catalyst (manifold).

Fig 1: Listen For An Exhaust Gas Leak

Courtesy of NISSAN MOTOR CO., U.S.A.

OK or NG

OK: GO TO 2.
NG: Repair or replace.