Supercharger boost pressure is regulated under certain conditions to prevent engine and drive train damage. When the engine is operating under high boost conditions, the engine control module (ECM) can limit boost pressure to 83 kPa (12 psi) or less.

The ECM disables boost under the following conditions:

The ECM controls boost pressure by a pulse-width ground signal to the boost control solenoid. The boost control solenoid is a normally open valve. Under most conditions, the ECM commands the boost control solenoid to operate at a 99-100 percent DC. This keeps the boost control solenoid valve closed and allows only inlet vacuum from the supercharger plenum to the bypass valve actuator 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. When the engine load is increased, the 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 measure is 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 DC, but may command a partial duty cycle, approximately 62 percent, depending on the operating conditions. This opens the boost control solenoid 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.

Schematic Reference

Engine Controls Schematics

Description and Operation

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Special Tools Required

J 35555 Metal Mityvac

1. Review the vacuum schematics in the Boost Control System Description. Refer to Boost Control System Description .
2. Ignition OFF, visually and physically inspect the supercharger components for any of the following conditions:

Inspect the vacuum lines for:

•

Cracking

•

Loose fit

•	Improper connections

•	Improper routing

3. Inspect the following components for damage, and for proper connections, adjustments, and installation:

•	The bypass valve actuator

•	The boost control solenoid

•	The bypass valve lever

•	The bypass valve cable--Refer to Supercharger Cleaning and Inspection .

4. Verify that the charge air cooler (CAC) coolant level is full.
5. Ignition ON, command the CAC coolant pump ON and OFF with a scan tool. Listen for the CAC coolant pump to turn ON and OFF with each command.

⇒	If the CAC coolant pump does not turn ON and OFF refer to Supercharger Intercooler Relay Diagnosis .

6. Engine running, command the supercharger bypass (SCB) solenoid from 0 to 90% with a scan tool. Observe the operation of the bypass valve, it should move as the DC percentages are varied.
7. Verify there are no vacuum leaks at the supercharger manifold gaskets and supercharger intake plenum.

1. Ignition OFF, disconnect the boost source hose from the boost control solenoid, connect the J 35555 to the boost source hose.
2. Engine running, observe the gage on the J 35555 for a reading equal to or greater then 15 inch Hg.

⇒	If less than 15 inch Hg, repair the boost vacuum source hose or the intake manifold port for a restriction or blockage.

3. Ignition OFF, connect the vacuum source hose to the boost solenoid.
4. Disconnect the boost signal hose from the bottom port of the bypass valve actuator and connect the J 35555 to the boost signal hose.
5. Engine running, observe the gage on the J 35555 for a reading of 0-1 inch Hg.

⇒	If greater than the specified range, replace the boost control solenoid.

6. Engine running, command the boost control solenoid to 0% DC with a scan tool. Observe the gage on the J 35555 for a reading equal to or greater than 15 inch Hg.

⇒	If less than the specified range, test the boost signal hose for a restriction or blockage. If the boost signal hose tests normal, replace the boost control solenoid.

7. Disconnect the inlet vacuum signal hose from the top of the bypass valve actuator, and connect J 35555 to the inlet vacuum signal hose.
8. Engine running, observe the gage on the J 35555 for a reading equal to or greater than 15 inch Hg.

⇒	If less than 15 inch Hg, repair the inlet vacuum signal hose or the intake manifold port for a restriction or blockage.

1. Ignition OFF, disconnect the inlet vacuum signal hose from the top of the bypass valve actuator.
2. Connect J 35555 to the inlet vacuum signal port at the bypass valve actuator.
3. Slowly apply 15 inch Hg of vacuum while observing the bypass valve actuator. The bypass valve actuator and cable should retract.

⇒	If the bypass valve actuator and cable do not retract, inspect the bypass valve and bypass valve actuator linkage for binding, sticking, or damage. If the bypass valve, cable, and linkage operate normally, replace the bypass valve actuator.

4. Connect the inlet vacuum signal hose to the top of the bypass valve actuator.
5. Disconnect the boost signal hose from the bottom of the bypass valve actuator, and connect J 35555 to the boost signal port on the bypass valve actuator.
6. Start and idle the engine in park.
7. Slowly apply vacuum until you reach 20 inch Hg, and observe the bypass valve actuator. The bypass valve actuator should extend.

⇒	If the bypass valve actuator does not extend, inspect the bypass valve and linkage for binding, sticking, or damage. If the bypass valve and linkage operate normally, replace the bypass valve actuator.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.