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For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2005 🢒 Cobalt 🢒 Engine 🢒 Engine Controls - 2.0L 🢒 Boost Control System Diagnosis

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 powertrain control module (PCM) can limit boost pressure to 83 kPa (12 psi) or less. The PCM disables boost under the following conditions:

    • When reverse gear is selected
    • When the vehicle is decelerating
    • If an intercooler pump failure is detected
    • If the intake air temperature (IAT) sensor 2 becomes excessively high
    • If the engine coolant temperature (ECT) becomes excessively high
    • Under heavy load in first and second gear at engine speeds above 5,800 RPM
    • 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 99-100 percent duty cycle. This keeps the 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 to overcome the diminishing 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 0-98 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: Engine Controls Schematics

Boost Control System Description: Boost Control System Description

1

Did you perform the Diagnostic System Check - Vehicle?

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Go to Step 2

Go to Diagnostic System Check - Vehicle

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.

  1. Turn OFF the ignition.
  2. Review the vacuum schematics in the Boost Control System Description.
  3. Inspect for the following conditions
    4. • The vacuum lines for any cracking, loose fit, and for the proper connections at the following:
       - The bypass valve actuator
       - The bypass valve solenoid
       - The supercharger intake plenum
       - The engine intake manifold
    • The bypass valve actuator for sticking, binding, or damage
    • The bypass valve lever for damage
    • The bypass valve linkage for sticking, binding, or damage
    • The boost control solenoid for damage

Did you find and correct the condition?

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Go to Step 15

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.
  4. Turn OFF all lights and accessories.

Is the vacuum at the specified value?

0 in Hg

Go to Step 4

Go to Step 10

4
  1. Select Boost Control in the Engine Output Controls.
  2. Command the Boost Control Solenoid to 0 percent duty cycle with a scan tool.
  3. Observe the vacuum gage.

Is the vacuum more than the specified value?

15 in Hg

Go to Step 5

Go to Step 8

5
  1. Reconnect the boost signal hose to the bypass valve actuator.
  2. Disconnect the inlet vacuum signal hose from the bypass valve actuator.
  3. Connect a vacuum gage to the inlet vacuum signal hose.

Is the vacuum more than the specified value?

15 in Hg

Go to Step 6

Go to Step 12

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, while observing the bypass valve actuator.

Does the bypass valve actuator retract?

18 in Hg

Go to Step 7

Go to Step 11

7
  1. Connect 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. Connect the boost signal hose to the bypass valve actuator.
  2. Disconnect the boost signal hose from the boost control solenoid.
  3. Connect a vacuum gage to the boost signal port on the boost control solenoid.
  4. Command the boost control solenoid to 0 percent duty cycle.

Is the vacuum more than the specified value?

15 in Hg

Go to Step 14

Go to Step 9

9
  1. Disconnect the boost source hose from the boost control solenoid.
  2. Connect a vacuum gage to the boost source hose.

Is the vacuum more than the specified value?

15 in Hg

Go to Step 10

Go to Step 13

10

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

Did you complete the replacement?

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Go to Step 15

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11

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

Did you complete the replacement?

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Go to Step 15

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12

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

Did you complete the repair?

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Go to Step 15

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13

Repair the boost source hose or the port for a restriction or blockage.

Did you complete the repair?

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Go to Step 15

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14

Repair the boost signal hose or the port for a restriction or blockage.

Did you complete the repair?

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Go to Step 15

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15
  1. Connect any disconnected components.
  2. Clear the DTCs with a scan tool.
  3. Turn OFF the ignition for 90 seconds.
  4. Operate the vehicle within the conditions necessary to verify the repair.

Did you verify the repair?

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Go to Step 16

Go to Step 2

16

Observe the Capture Info with a scan tool.

Are there any DTCs that have not been diagnosed?

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Go to Diagnostic Trouble Code (DTC) List - Vehicle

System OK