GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Buick 🢒 2003 🢒 Regal 🢒 Engine 🢒 Engine Controls - 3.8L 🢒 Boost Control System Diagnosis

Circuit Description

Supercharger boost pressure is regulated to prevent engine and drive train damage. When the engine is operating under high boost conditions, the powertrain control module (PCM) limits boost pressure to 8 psi. The PCM disables boost under the following conditions:

    • When reverse gear is selected
    • When the vehicle is decelerating
    • When the engine coolant temperature is excessively high
    • When drivetrain abuse is detected

The PCM controls boost pressure by using the boost control solenoid. The boost control solenoid is a normally open valve. Under most conditions, the PCM commands the boost control solenoid to operate at a 100% 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 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. When reduced boost pressure is desired, the PCM commands the boost control solenoid to operate at a 0 percent duty cycle. 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 recirculating excess boost pressure back into the supercharger inlet.

Step

Action

Values

Yes

No

Schematic Reference: Boost Control System Description

1

Did you perform the Diagnostic System Check-Engine Controls?

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Go to Step 2

Go to Diagnostic System Check - Engine Controls

2

Important: This diagnostic assumes that the engine is in satisfactory mechanical condition and able to provide sufficient vacuum to operate the boost control system.

Inspect the following items and repair any condition as necessary:

    • The vacuum lines for cracking, and loose fit
    • The bypass valve actuator for sticking, binding, or damage
    • The bypass valve for sticking, binding, or damage
    • The bypass valve linkage for binding or damage
    • The boost control solenoid for damage

Did you find and correct the condition?

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Go to Step 16

Go to Step 3

3
  1. Disconnect the boost signal hose from the bypass valve actuator.
  2. Connect a vacuum gage to the boost signal hose.
  3. Start and idle the engine in park.

Does the vacuum gage read near the specified value?

0 in Hg

Go to Step 4

Go to Step 10

4
  1. Connect a scan tool and command the boost control solenoid to 0 percent duty cycle.
  2. Observe the vacuum gage.

Does the vacuum gage read more than the specified value?

15 in Hg

Go to Step 5

Go to Step 8

5
  1. Turn OFF the ignition.
  2. Reconnect the boost signal hose to the bypass valve actuator.
  3. Disconnect the inlet vacuum signal hose from the bypass valve actuator.
  4. Connect a vacuum gage to the inlet vacuum signal hose.
  5. Start and idle the engine in park.

Does the vacuum gage read more than the specified value?

15 in Hg

Go to Step 6

Go to Step 13

6
  1. Turn OFF the ignition.
  2. Connect a vacuum pump to the inlet vacuum signal port on the bypass valve actuator.
  3. Slowly apply vacuum to the specified value.

Does the bypass valve actuator retract?

15 in Hg

Go to Step 7

Go to Step 11

7
  1. Reconnect the inlet vacuum signal hose to the bypass valve actuator.
  2. Disconnect the boost signal hose from the bypass valve actuator.
  3. Connect a vacuum pump to the boost signal port on the bypass valve actuator.
  4. Start and idle the engine in park.
  5. Slowly apply vacuum to the specified value.

Does the bypass valve actuator extend?

20 in Hg

System OK

Go to Step 11

8
  1. Turn OFF the ignition.
  2. Reconnect the boost signal hose to the bypass valve actuator.
  3. Disconnect the boost signal hose from the boost control solenoid.
  4. Connect a vacuum gage to the boost signal port on the boost control solenoid.
  5. Start and idle the engine in park.
  6. Command the boost control solenoid to 0 percent duty cycle.

Does the vacuum gage read more than the specified value?

15 in Hg

Go to Step 15

Go to Step 9

9
  1. Turn OFF the ignition.
  2. Disconnect the boost source hose from the boost control solenoid.
  3. Connect a vacuum gage to the boost source hose.
  4. Start and idle the engine in park.

Does the vacuum gage read more than the specified value?

15 in Hg

Go to Step 10

Go to Step 14

10

Replace the boost control solenoid. Refer to Boost Control Solenoid Replacement .

Did you complete the replacement?

--

Go to Step 16

--

11

Inspect the bypass valve and bypass valve actuator linkage for binding, sticking or damage. Repair any condition as necessary.

Did you find and correct a condition?

--

Go to Step 16

Go to Step 12

12

Replace the bypass valve actuator. Refer to Supercharger Bypass Valve Actuator Replacement .

Did you complete the replacement?

--

Go to Step 16

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13

Repair the inlet vacuum signal hose for a restriction or blockage.

Did you complete the repair?

--

Go to Step 16

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14

Repair the boost source hose for a restriction or blockage.

Did you complete the repair?

--

Go to Step 16

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15

Repair the boost signal hose for a restriction or blockage.

Did you complete the repair?

--

Go to Step 16

--

16
  1. Reconnect any disconnected components.
  2. Use the scan tool in order to clear any DTCs that may have set.
  3. Turn OFF the ignition for 30 seconds.
  4. Operate the vehicle within conditions to verify the repair.

Did you verify the repair?

--

Go to Step 17

Go to Step 2

17

With a scan tool, observe the stored information, Capture Info.

Does the scan tool display any DTCs that you have not diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List

System OK