CTS RWD V8-6.2L SC (2009)
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Vehicle speeds exceed 159 mph in third, second, and fourth gears only, after 150 seconds boost is trimmed actively.
The ECM controls boost pressure by using the boost control solenoid. The boost control solenoid is normally an open valve. Under most conditions, the
ECM commands the boost control solenoid to operate at a 99-100 percent duty cycle. This keeps the solenoid valve closed and allows only inlet vacuum
to control the position of the bypass valve. At idle, engine vacuum is applied to the upper side of the bypass valve actuator, counteracting spring tension
to hold the bypass valve open. As engine load is increased, engine vacuum is decreased, causing the spring in the bypass valve actuator to overcome the
applied vacuum, closing the bypass valve and allowing the boost pressure to increase. The bypass valve starts to close when the vacuum measures 250
mm Hg (10 in Hg) and is fully closed at 90 mm Hg (3.5 in Hg). When reduced boost pressure is desired, the ECM commands the boost control solenoid
to operate at a 0 percent duty cycle, but may command a partial duty cycle, approximately 62 percent, depending on the operating condition. This opens
the solenoid valve and allows boost pressure to enter the bypass valve actuator at the lower side to counteract the spring tension, opening the bypass
valve and re-circulating excess boost pressure back into the supercharger inlet.
Results of Incorrect Operation
The following conditions will result in reduced engine power, especially during a wide open throttle (WOT) operation:
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An open boost control solenoid control circuit.
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An open control solenoid ignition 1 voltage circuit.
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An open control solenoid control circuit.
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A boost control solenoid valve that is stuck open.
The following conditions will result in full boost to be commanded at all times. These conditions can also result in overboost conditions during high
engine load situations.
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A boost control solenoid control circuit shorted to ground.
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A boost control solenoid valve is stuck closed.
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A restriction in the boost source or signal vacuum hoses.
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A restriction in the exhaust system may cause an overboost condition and reduced fuel economy.
A restriction in the vacuum signal hose to the bypass valve actuator or stuck closed bypass valve will cause a noisy idle and reduced fuel economy.
