Colorado 4WD L5-3.7L (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 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 powertrain control module (PCM). The PCM sends a pulse width modulated 12-volt
signal to a CMP actuator solenoid in order to control the amount of engine oil flow to a Cam Phaser passage. There are 2 different passages for oil to
flow through, a passage for cam advance and a passage for cam retard. The Cam Phaser is attached to a camshaft and is hydraulically operated in order
to change the angle of the camshaft relative to crankshaft position (CKP). Engine oil pressure (EOP), viscosity, temperature and engine oil level can have
an adverse affect on Cam Phaser performance. The PCM calculates the optimum cam position through the following inputs:
* Engine speed
* Manifold absolute pressure (MAP)
* Throttle position indicated angle
* CKP
* CMP
* Engine load
* Barometric (BARO) pressure
The Cam Phaser default position is 0 degrees. The PCM uses the following inputs before assuming control of the Cam Phaser:
* 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 pressure
CMP Actuator Solenoid Circuit Diagnostics
The powertrain control module (PCM) monitors the control circuits of the camshaft position (CMP) actuator solenoid for electrical faults. The PCM has
the ability to determine if a control circuit is open, shorted high, and shorted low. If the PCM detects a fault with a CMP actuator solenoid circuit, a DTC
will set.
CMP Actuator System Performance Diagnostics
The powertrain control module (PCM) monitors the performance of the camshaft position (CMP) actuator system by monitoring the actual and desired
positions of a Cam Phaser. 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.
