Test Description

WARNING: This page is about a different car, the 1995 Oldsmobile Ninety-Eight and 1995 Buick Park Avenue. However, it is still accessible from the selected car via links, so may be relevant.

NOTE: Test numbers refer to numbers on diagnostic chart.

Circuit shorted to ground will keep by-pass valve closed when PCM is commanding it open, possibly causing an overboost condition during high engine load situations.
No inlet vacuum to by-pass valve actuator may cause by-pass valve to remain closed during deceleration. This condition may be perceived as a sail-on, possibly accompanied by a rough idle.

Fig 1: Code P1257 Schematic (3.8L - VIN 1) Boost Control Problem

Fig 2: Code P1257 Diagnostic Flow Chart (3.8L - VIN 1) Boost Control Problem