How to turn on auto focus mode on nikon d90?

Auto focus mode on nikon d90 sometimes gets deactivated and i have difficulty turning it back on

There's no autofocus mode on-off menu setting on the D90. You turn autofocus on or off by either selecting the rotary switch (located on the lower left front of the camera) labelled AF M to "AutoFocus" or "Manual", or if the lens has an auto or manual selector.

You can change auto focus mode to AF-S, AF-C, or AF-A (Auto) by depressing and holding the AF button (located to the right of the top display), while turning the rear command dial.

Finally, you can change the parameters of the autofocus setting, such as dynamic or spot focusing, and a host of other options from the "a" custom menu.

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