A valve timing control system for an internal combustion engine is provided,
which
includes: a crank angle sensor detecting a crank angle corresponding to an internal
combustion engine crank shaft rotational angle; an actuator relatively modifying
phases of a cam angle with the crank angle; a cam angle sensor detecting the cam
angle modified by the actuator; an oil control valve driving the actuator; a target
value detection unit calculating a target value according to the internal combustion
engine operation state; a cam angle control unit controlling the detected cam angle
to coincide with the calculated target value; a learning unit learning a control
signal to the oil control valve when the cam angle substantially coincides with
the target value; and a failure detection unit detecting failure of the actuator.
The failure detection unit modifies a failure detection condition according to
whether learning is performed in the learning unit.
