TrailBlazer 2WD L6-4.2L VIN S (2003)
Camshaft Position Sensor: Description and Operation
Camshaft Actuator System
CAMSHAFT POSITION (CMP) ACTUATOR SYSTEM
The Camshaft Position Actuator system is used for a variety of engine performance enhancements. These enhancements include lower emission output
through exhaust gas recirculation 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 CMP Actuator system is controlled by the Powertrain Control Module (PCM). The PCM sends a pulse width modulated 12 volt signal to a
Camshaft Position (CMP) Actuator Solenoid in order to control the amount of engine oil flow to a cam Phaser passage. There are two 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. Engine oil pressure, 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:
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Engine Speed
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Manifold Absolute Pressure (MAP)
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Throttle Position (TP) Indicated Angle
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Crankshaft Position (CKP)
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Camshaft Position (CMP)
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Engine Load.
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Barometric (BARO) Pressure
The Cam Phaser default position is 0 degrees. The PCM uses the following inputs before assuming control of the cam phaser:
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Engine Coolant Temperature (ECT)
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Closed Loop Fuel Control
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Engine Oil Temperature
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Engine Oil Pressure
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Engine Oil Level
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CMP Actuator Solenoid circuit state
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Ignition 1 signal voltage
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Barometric (BARO) Pressure
CMP ACTUATOR SOLENOID CIRCUIT DIAGNOSTICS
The PCM monitors the control circuits of the 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 Diagnostic Trouble Code (DTC) will set.
CMP ACTUATOR SYSTEM PERFORMANCE DIAGNOSTICS
The PCM monitors the performance of the 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.
