G6 L4-2.4L (2007)
Variable Valve Timing Actuator: Description and Operation
Camshaft Actuator System Description
Camshaft Position (CMP) Actuator System
The camshaft position (CMP) actuator system is used on both the intake and exhaust camshafts. The CMP actuator system is used for a variety of engine
performance enhancements. These enhancements include lower emission output through exhaust gas recirculation (EGR) control, a wider engine torque
range, improved gas millage, and improved engine idle stability. The CMP actuator system accomplishes this by controlling the amount of intake and
exhaust valve overlap.
CMP Actuator System Operation
The camshaft position (CMP) actuator system is controlled by the control module. The control module sends a pulse width modulated 12-volt signal to
each CMP actuator solenoid to control the amount of engine oil flow to a camshaft actuator passage. There are 2 different passages for oil to flow
through, a passage for camshaft advance and a passage for camshaft retard. The camshaft actuator is attached to each camshaft and is hydraulically
operated to change the angle of each camshaft relative to crankshaft position (CKP). Engine oil pressure (EOP), viscosity, temperature, and engine oil
level can affect camshaft actuator performance. The control module calculates the optimum camshaft position through the following inputs:
* Engine speed
* Manifold absolute pressure (MAP)
* Throttle position indicated angle
* CKP
* CMP
* Engine load
* Barometric pressure (BARO)
A locking pin keeps the CMP actuators in the parked position to avoid valve train noise upon engine start-up. The parked position is 0 degrees of
camshaft actuation. The locking pin will release the actuator after the EOP is sufficient to overcome the locking pin spring pressure. The exhaust CMP
actuators also have return springs. The return springs are necessary to assist the CMP actuators to return to the parked position due to the rotational
inertia of the valve train components upon engine shutdown. The control module uses the following inputs before assuming control of the CMP actuator:
* Engine coolant temperature (ECT)
* Closed loop fuel control
* Engine oil temperature (EOT)
* EOP
* Engine oil level
* CMP actuator solenoid circuit state
* Ignition 1 signal voltage
* BARO
CMP Actuator Solenoid Circuit Diagnostics
The control module monitors the control circuits of the camshaft position (CMP) actuator solenoid for electrical faults. The control module has the
ability to determine if a control circuit is open, shorted high, and shorted low. If the control module detects a fault with a CMP actuator solenoid circuit,
a DTC will set.
CMP Actuator System Performance Diagnostics
The control module monitors the performance of the camshaft position (CMP) actuator system by monitoring the actual and desired position of the CMP
sensor. If the difference between the actual and desired position is more than a calibrated angle for more than a calibrated amount of time, a DTC will
set.
