Exhaust System Backpressure
WARNING: This page is about a different car, the 2003 Pontiac Grand Prix, 2003 Chevrolet Malibu, and 2003 Buick Century. However, it is still accessible from the selected car via links, so may be relevant.
For exhaust system backpressure check, go to EXHAUST RESTRICTION under EXHAUST SYSTEM CHECK under EMISSIONS SYSTEM & SUB-SYSTEMS in SYSTEM & COMPONENT TESTING - 3.1L CENTURY, GRAND PRIX & MALIBU article.