Powertrain Controls - ECM/PCM

CIRCUIT DESCRIPTION
On turbo charged engines, the exhaust gases pass from the exhaust manifold through the turbocharger, turning the turbine blades. The compressor side of the turbocharger also turns, pulling air through the air filter and pushing the air into the intake manifold, pressurizing the intake manifold.

The wastegate is normally closed, but opens to bypass exhaust gas to prevent an overboost condition. The wastegate will open when pressure is applied to the actuator, and is controlled by a wastegate control solenoid valve pulsed "ON" and "0FF" by the ECM Under normal driving conditions, the control solenoid is energized all the time which closes "OFF" the manifold pressure to the wastegate actuator. This allows for a rapid increase in boost pressure. A boost increase will be detected by the MAP sensor, and the ECM will pulse the wastegate control valve. Manifold pressure will then be allowed to pass to the wastegate actuator, and the actuator will open the wastegate. This will prevent an overboost condition on heavy acceleration. As boost pressure decreases, the ECM closes the control valve and the wastegate actuator pressure bleeds "OFF" through the vent in the control valve. If an overboost does exist as indicated by the MAP sensor, the ECM will reduce fuel delivery to prevent damage to the engine.

If the level of coolant in the charge air cooler (CAC) is low, the turbo boost cut-out relay will shut off all power to the wastegate solenoid, causing the wastegate to close. The "LOW TURBO COOLANT" lamp will remain "ON" until coolant is added. To add turbo coolant, refer to "TURBOCHARGER."


TEST DESCRIPTION
Numbers below refer to circled numbers on the diagnostic chart.
1. A Code 31 will set when the manifold absolute pressure exceeds 205 kPa of boost for two seconds, and a Code 33 has not previously been set. Code 31 will set, but the "Check Engine" light will stay "ON" only while the overboost exists. The light will stay "ON" for 10 seconds after the condition exists and then go "OUT."
An overboost condition could be caused by:
^ CKT 471 shorted to ground,
^ A sticking wastegate actuator or wastegate,
^ A control valve stuck in the closed position,
^ A cut or pinched hose,
^ A faulty ECM,
^ An extremely dirty air filter,
With ignition shut "OFF," the control valve solenoid is open.
2. After the 103 kPa (15 psi) is applied to valve and then the pressure source is removed, the actuator should slowly move back and close the wastegate. If the pressure does not bleed "OFF," the vent in the control valve solenoid could be plugged.
3. With the ignition "ON" and the diagnostic terminal grounded, the control valve solenoid should be energized. This closes "OFF" the manifold to the wastegate actuator.
4. Check the electrical control portion of the system. With key "ON" and engine not running, the solenoid should not be energized.