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 mileage, and improved engine idle stability. The CMP actuator system accomplishes this by controlling the amount of intake and exhaust valve overlap. The Park position for the CMP actuator and camshaft is 8.5 degrees before top dead center (BTDC) or 17 crankshaft degrees BTDC. The engine control module (ECM) can only command the CMP actuator to retard the valve timing from the Park position or advance the valve timing back to the Park position. The total range of valve timing authority is 31 degrees camshaft rotation, or 62 degrees of crankshaft rotation. The control range is from the Park position of 8.5 degrees camshaft or 17 degrees crankshaft BTDC, to 22.5 degrees camshaft or 45 degrees crankshaft after top dead center (ATDC).

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 V signal to a CMP actuator solenoid in order 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 cam advance and a passage for cam retard. The camshaft actuator is attached to the front of the camshaft and is hydraulically operated in order to change the angle of the camshaft relative to crankshaft position (CKP). Incorrect engine oil pressure (EOP), viscosity, temperature, engine oil level, or aftermarket engine oil additives can have an adverse affect on camshaft actuator performance.

CMP Actuator Solenoid Circuit Diagnostics

The engine control module (ECM) monitors the control circuit 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, or shorted low. If the control module detects a fault with the CMP actuator solenoid control circuit, DTC P0010 will set.

CMP Actuator System Performance Diagnostic

The engine control module (ECM) monitors the performance of the camshaft position (CMP) actuator system by monitoring the calibrated desired position and the actual position of the camshaft through the 4X signal of the CMP sensor. If the difference between the actual and desired position is greater than a calibrated angle for a calibrated amount of time, DTC P0011 will set.