Powertrain Controls - ECM/PCM

Boost Control Solenoid Circuit:

CIRCUIT DESCRIPTION
Under most conditions, the boost solenoid operates at 100% duty cycle ("ON" all the time) to allow maximum boost pressure on demand. However, under certain other conditions, such as when reverse gear is selected, or during rapid deceleration, the duty cycle is cut-off, which limits manifold pressure to near atmospheric. Under these conditions, the PCM commands the boost pressure solenoid to operate at 0% duty cycle ("OFF"), which opens the bypass valve and allows pressurized manifold air to escape back to the inlet side of the supercharger. When the engine is under heavy load, the duty cycle is maintained at a % "ON" time that will regulate boost pressure to a level the engine can tolerate without damage.

If the PCM detects a malfunction of the solenoid that would cause the engine to "over-boost", the Service Engine Soon (SES) light will come "ON" and a code 57 will set.

TEST DESCRIPTION

Code 57 Diagnostic Chart:

Numbers below refer to circled numbers on diagnostic chart.

1. Circuit 922 shorted to ground will keep the bypass valve "CLOSED" when the PCM is commanding it "OPEN", possibly causing an overboost condition during high engine load situations.
2. No inlet vacuum to the bypass actuator may cause the bypass valve to remain closed during deceleration. This condition will be perceived as a "sail-on" (take your foot off the gas but the engine does not slow down), possibly accompanied by a rough idle.
3. Checks for a sticking boost control solenoid.