A control system (40, 80) for varying cylinder valve timing of an internal combustion engine that has a pump (42, 82), a reservoir (44, 84), a crankshaft, and a camshaft; said control system comprising: a first cam phase actuator (68, 104) for adjusting a rotational phase of the camshaft relative to the crankshaft and having a first actuator port (66, 106) and a second actuator port (70, 108); a first control valve (46, 86) comprising a first port (53, 92) operatively connected to receive fluid from the pump, a second port (55, 94) in fluid communication with the second actuator port, and a first workport (54, 93) in fluid communication with the first port of the first cam phase actuator, the first control valve having a first position in which a first fluid path is provided between the first port and the first workport, and having a second position in which a second fluid path is provided between the second port and the first workport; a second control valve (48, 88) comprising a third port (57, 96) operatively connected to receive fluid from the pump, a fourth port (59, 98) in fluid communication with the first actuator port, and a second workport (58, 97) in fluid communication with the second actuator port, the second control valve having one position in which a third fluid path is provided between the third port and the second workport, and having another position in which a fourth fluid path is provided between the fourth port and the second workport; a first check valve (50, 90)operatively connected to restrict fluid to flow through the first path only in a direction from the pump to the first cam phase actuator; a second check valve (52, 91) operatively connected to restrict fluid to flow through the third path only in a direction from the pump to the first cam phase actuator; a third check valve operatively connected to restrict fluid to flow only in a direction from the second port to the second actuator port; and a fourth check valve operatively connected to restrict fluid to flow only in a direction from the fourth port to the first actuator port. a first cam phase actuator (68, 104) for adjusting a rotational phase of the camshaft relative to the crankshaft and having a first actuator port (66, 106) and a second actuator port (70, 108); a first control valve (46, 86) comprising a first port (53, 92) operatively connected to receive fluid from the pump, a second port (55, 94) in fluid communication with the second actuator port, and a first workport (54, 93) in fluid communication with the first port of the first cam phase actuator, the first control valve having a first position in which a first fluid path is provided between the first port and the first workport, and having a second position in which a second fluid path is provided between the second port and the first workport; a second control valve (48, 88) comprising a third port (57, 96) operatively connected to receive fluid from the pump, a fourth port (59, 98) in fluid communication with the first actuator port, and a second workport (58, 97) in fluid communication with the second actuator port, the second control valve having one position in which a third fluid path is provided between the third port and the second workport, and having another position in which a fourth fluid path is provided between the fourth port and the second workport; a first check valve (50, 90)operatively connected to restrict fluid to flow through the first path only in a direction from the pump to the first cam phase actuator; a second check valve (52, 91) operatively connected to restrict fluid to flow through the third path only in a direction from the pump to the first cam phase actuator; a third check valve operatively connected to restrict fluid to flow only in a direction from the second port to the second actuator port; and a fourth check valve operatively connected to restrict fluid to flow only in a direction from the fourth port to the first actuator port.