Component Tests and General Diagnostics
Boost Control System Diagnosis
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis Strategy Based Diagnosis for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions Diagnostic Procedure Instructions provides an overview of each diagnostic category.
Circuit Description
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:
* Reverse gear is selected.
* An intercooler pump failure is detected.
* An electronic throttle control fault is detected.
* Intake air temperature (IAT) sensor 2 is equal to or greater than 120.5°C (248°F) boost pressure is limited to 145 kPa (7 psi). The ECM commands the boost control solenoid to 62 % duty cycle.
* Engine coolant temperature (ECT) is greater than 125°C (257°F).
* Drivetrain abuse is detected.
* Vehicle speeds exceed 256 km/h (159 mph) in second, third or fourth gear for greater than 150 s.
The ECM controls boost pressure by a pulse-width modulated (PWM) 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 % duty cycle. 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 10 in Hg and is fully closed at 3.5 in Hg. When reduced boost pressure is desired, the ECM commands the boost control solenoid to operate at a 0 % duty cycle, but may command a partial duty cycle, approximately 62 %, 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.
Reference Information
Schematic Reference
Engine Controls Schematics [1][2]Electrical Diagrams
Connector End View Reference
Component Connector End Views Connector Views
Description and Operation
* Supercharger Description and Operation Supercharger
* Boost Control System Description Description and Operation
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions Powertrain Diagnostic Trouble Code (DTC) Type Definitions
Scan Tool Reference
Control Module References Control Module References for scan tool information
Special Tools
J-23738-A Mityvac
Circuit/System Verification
1. Verify that the charge air cooler coolant is at the proper level. Refer to Charge Air Cooling System Coolant Level Inspection Charge Air Cooling System Coolant Level Inspection.
2. Verify that the vacuum lines to the supercharger components are properly routed. Refer to Boost Control System Description Description and Operation.
3. Verify the following conditions do not exist with the supercharger system:
* Damaged or improperly installed boost control solenoid
* Damaged, restricted or improperly installed bypass valve actuator
* Damaged, restricted or improperly installed bypass valve linkage
* Leaks at the supercharger manifold gaskets and supercharger intake plenum.
• If a condition is found, repair or replace the affected component as necessary. Refer to Supercharger Cleaning and Inspection 63. Supercharger Cleaning and Inspection.
4. Ignition ON, command the CAC coolant pump ON and OFF with a scan tool. The charge air cooler coolant pump should turn ON and OFF with each command.
• If the charge air cooler coolant pump does not turn ON and OFF refer to Supercharger Intercooler Relay Diagnosis Testing and Inspection.
5. Engine running, command the SCB solenoid between 0-90 % with a scan tool while observing the bypass valve. The bypass valve should move as the duty cycle percentages are varied.
Circuit/System Testing
1. Ignition OFF, disconnect the boost source hose from the boost control solenoid, connect the J-23738-A to the boost source hose.
2. Engine running, observe the gauge on the J-23738-A for a reading of at least 15 in Hg.
• If less than 15 in Hg, test the boost vacuum source for proper operation and test the vacuum source hose and the intake manifold port for a restriction or blockage.
3. Ignition OFF, connect the vacuum source hose to the boost control solenoid.
4. Disconnect the boost signal hose from the bottom port of the bypass valve actuator and connect the J-23738-A to the boost signal hose.
5. Engine running, observe the gauge on the J-23738-A for a reading of 0-1 in Hg.
• If greater than the specified range, replace the boost control solenoid.
6. Engine running, command the boost control solenoid to 0% duty cycle with a scan tool. Observe the gauge on the J-23738-A for a reading of at least 15 in 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 the J-23738-A to the inlet vacuum signal hose.
8. Engine running, observe the gauge on the J-23738-A for a reading of at least 15 in Hg.
• If less than the specified range, test the inlet vacuum signal hose and the intake manifold port for a restriction or blockage.
Component Testing
1. Ignition OFF, disconnect the inlet vacuum signal hose from the top of the bypass valve actuator.
2. Connect the J-23738-A to the inlet vacuum signal port at the bypass valve actuator.
3. Slowly apply 15 in Hg of vacuum while observing the bypass valve actuator. The bypass valve actuator should retract.
• If the bypass valve actuator does not operate as specified, inspect the bypass valve actuator and linkage for binding, sticking or damage. If the bypass valve linkage operates 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 the J-23738-A 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 in Hg, and observe the bypass valve actuator. The bypass valve actuator should extend.
• If the bypass valve actuator does not operate as specified, inspect the bypass valve and linkage for binding, sticking, or damage. If the bypass valve and linkage operate normally, replace the bypass valve actuator.
Repair Instructions
Perform the Diagnostic Repair Verification Verification Tests after completing the diagnostic procedure.
* Charge Air Bypass Regulator Solenoid Valve Replacement Service and Repair
* Supercharger Bypass Valve Actuator Replacement Supercharger Bypass Valve Actuator Replacement