Chart C-18 Boost Control Solenoid Functional Check

Chart C-18, Boost Control Functional Check (1 Of 2):

Chart C-18, Boost Control Solenoid Functional Check (2 Of 2):

Boost Control Solenoid Circuit:

CIRCUIT DESCRIPTION
The Boost Control solenoid valve is a normally open, electrically operated vacuum/pressure valve that regulates manifold pressure to the bypass valve actuator.

When the solenoid is closed (energized), manifold pressure to the bypass valve actuator is blocked, allowing maximum boost. When the solenoid is open (de-energized), manifold pressure acts against the diaphragm of the bypass valve actuator, opening the bypass valve. With the valve open, pressurized air from the manifold is vented to the inlet side of the supercharger, reducing manifold pressure.

The solenoid is controlled by the computer. It gets battery power when the ignition is turned "ON" and becomes energized when the PCM completes the circuit to ground. The PCM operates the solenoid on a duty cycle (% "ON" time Vs. % "OFF" time.) Under most conditions, the boost solenoid operates at 100% duty cycle ("ON" all the time) to allow maximum boost pressure on demand. However, under certain other conditions, such as when reverse gear is selected, or during rapid deceleration, the duty cycle is cut-off, which limits manifold pressure to near atmospheric. Under these conditions, the PCM commands the boost pressure solenoid to operate at 0% duty cycle. When the engine is under heavy load, the duty cycle is maintained at a % "ON" time that will regulate boost pressure to a level the engine can tolerate without damage.

TEST DESCRIPTION
Numbers below refer to circled numbers on diagnostic charts.
1. Checks to verify battery power is available to the solenoid.
2. Checks to see if the PCM is able to complete the solenoid circuit to ground.
3. Checks for faulty solenoid (open or sticking).
4. Checks for faulty (restricted) boost control solenoid valve or restriction in boost system signal hoses.

DIAGNOSTIC AIDS
An intermittent may be caused by a poor connection, worn through wire insulation, or a wire broken inside the insulation. Check for the following.

^ Poor connection or damaged harness.
Inspect PCM harness connectors for backed out terminals, improper mating, broken connector locks, improperly formed or damaged terminals, poor terminal to wire connections (terminal crimped onto insulation), or damaged harness.

^ Intermittent Test
If problem is intermittent and connections and harness check OK, connect a digital voltmeter to the affected terminal and ground and move the harness around (wiggle/pull test). If there is a broken wire or intermittent poor connection, the voltage reading will change when the fault is re-created.