Code P1257, Boost Control Problem: Notes

Under most conditions, PCM commands boost control solenoid to operate at a 100 percent duty cycle (on) to allow full intake boost pressure upon demand. However, if reverse gear is selected, PCM detects rapid deceleration, or engine load is extremely high, reduced boost is desired. Under these conditions, PCM commands boost control solenoid to operate at a zero percent duty cycle (off), which opens by-pass valve to reduce boost pressure by recirculating it back through supercharger inlet. Code P1257 will set when the following conditions are present.

• Intake air temperature is greater than 0 °F (-18°C).
• Boost duty cycle less than 100 percent.
• Engine torque exceeds a calibrated maximum torque value. This value varies depending on commanded gear and engine RPM.
• Above conditions for at least 6 seconds.

Code P1257 will set if a malfunction in boost control system that causes engine torque to be too high (by-pass valve not opening) exists. PCM will illuminate Malfunction Indicator Light (MIL).

1. 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.
2. 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.