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The CVVT (Continuously Variable Valve Timing) system is installed to the chain sprocket of the intake camshaft. This system controls the intake camshaft to provide the optimal valve timing for every driving condition. The PCM controls the Oil Control Valve(OCV), based on the signals output from mass air flow, throttle position and engine coolant temperature. The CVVT controller regulates the intake camshaft angle using oil pressure through the OCV. As result, the relative position between the camshaft and the crankshaft becomes optimal, and the engine torque improves, fuel economy improves, exhaust emissions decrease under overall driving conditions.

Figure1. illustrates the method for detecting unresolved phasing steady-state error.

The figure shows two cases, case 1 to the left of the dashed line, and case 2 to the right of the dashed line. In case 1,the duty cycle command is considered high, or above a calibration threshold memorized in PCM. This should cause the cam phaser to move toward the maximum position, but the position remains at a medium level. The range of positions considered ‘medium’ is defined by calibrations.

In case 2, the duty cycle command is considered low, or below a calibration threshold memorized in PCM. This should cause the cam phaser to move toward the minimum position, but the position remains at a medium level.

Each of these cases is a phaser position error failure. Each case is also considered to be due to a phaser seizure. When either case is detected, a timing counter begins to increment. If the counter exceeds a calibration threshold memorized in PCM, the failure criteria is TRUE.

Another similar diagnostic test is performed to check steady-state error. In this test, no consideration is given to the duty cycle command versus phaser position. This test is only a check of the phasing position error. In the test, if the phaser error is greater than a calibration threshold memorized in PCM,a timing counter increments. If the counter exceeds the calibration threshold memorized in PCM,the failure criteria is TRUE.

PCM monitors CAM phaser error while both cam offset is available and cam velocity is below 15CAD/s .If the CAM phaser does not move although PCM commands OCV duty cycle, PCM determines that a fault exists and a DTC is stored.