intermittently have usage of 4 wheel drive.

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Intermittently, my selector switch blinks during start-up but then no lights stay lit (2w, auto, 4w). At that time the actuator doesn't engage in the transfer case and the 4 wheel drive doesn't work . The problem initially began by not physically shifting into 4w drive even when the selector switch was lit, although in auto 4w it would engage when the wheels began to slip. The only codes are CO455(steering wheel angle sensor) and D0442 (emission issue).