turn on wifi hotspot

You should be able to do it in Android 4.2 make sure you have the permission

android.permission.CHANGE_WIFI_STATE

and we cannot help you unless you post your code.

I believe this will help you check if tethering is active

    WifiManager wifiManager = (WifiManager) getSystemService(WIFI_SERVICE);

    Method[] methods = wifiManager.getClass().getDeclaredMethods();
    for (Method method : methods) {
        if (method.getName().equals("setWifiApEnabled")) {
            try {
                method.invoke(wifiManager, null, enable);
            } catch (Exception ex) {
            }
            break;
        }
    }

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