Variable Camshaft Timing (VCT) System: Overview

The intake phase shifting (IPS) VCT system enables rotation of the intake camshaft relative to the crankshaft rotation as a function of engine operating conditions.

The VCT system has several operational modes: idle, part throttle, wide open throttle (WOT), and default mode. At idle and low engine speeds with closed throttle, the PCM determines the phase angle based on airflow, engine oil temperature and engine coolant. At part and wide open throttle the PCM determines the phase angle based on engine RPM, load, and throttle position. VCT systems provide reduced emissions and enhanced engine power, fuel economy and idle quality. The VCT system also has the added benefit of improved torque.

The VCT system knocking and noise concerns are diagnosed in the Service Information. For additional information, refer to the Engine System - General Information article. Verification of incorrect VCT phasing on a warm engine operating below 1500 RPM can be isolated using a stethoscope and by monitoring the PIDs using a scan tool. If the VCT phaser does not maintain correct valve timing, low oil pressure or oil flow restrictions are primary possible causes. Verify correct oil pressure and flow, refer to the Engine System - General Information article.