有些機油用小米4電信4G版刷了cm13後 不能切換4G 3G訊號（現預設已修復），這裡給出解決方法。

1.先root手機

2.修改build.prop，找到ro.telephony.default_network= 這一行，修改這行的值，以下給出每個值對應的訊號：

/* NETWORK_MODE_* See ril.h RIL_REQUEST_SET_PREFERRED_NETWORK_TYPE */
int NETWORK_MODE_WCDMA_PREF     = 0; /* GSM/WCDMA (WCDMA preferred) */
int NETWORK_MODE_GSM_ONLY       = 1; /* GSM only */
int NETWORK_MODE_WCDMA_ONLY     = 2; /* WCDMA only */
int NETWORK_MODE_GSM_UMTS       = 3; /* GSM/WCDMA (auto mode, according to PRL)
                                        AVAILABLE Application Settings menu*/
int NETWORK_MODE_CDMA           = 4; /* CDMA and EvDo (auto mode, according to PRL)
                                        AVAILABLE Application Settings menu*/
int NETWORK_MODE_CDMA_NO_EVDO   = 5; /* CDMA only */
int NETWORK_MODE_EVDO_NO_CDMA   = 6; /* EvDo only */
int NETWORK_MODE_GLOBAL         = 7; /* GSM/WCDMA, CDMA, and EvDo (auto mode, according to PRL)
                                        AVAILABLE Application Settings menu*/
int NETWORK_MODE_LTE_CDMA_EVDO  = 8; /* LTE, CDMA and EvDo */
int NETWORK_MODE_LTE_GSM_WCDMA  = 9; /* LTE, GSM/WCDMA */
int NETWORK_MODE_LTE_CMDA_EVDO_GSM_WCDMA = 10; /* LTE, CDMA, EvDo, GSM/WCDMA */
int NETWORK_MODE_LTE_ONLY       = 11; /* LTE Only mode. */
int NETWORK_MODE_LTE_WCDMA      = 12; /* LTE/WCDMA */
int NETWORK_MODE_TD_SCDMA_ONLY            = 13; /* TD-SCDMA only */
int NETWORK_MODE_TD_SCDMA_WCDMA           = 14; /* TD-SCDMA and WCDMA */
int NETWORK_MODE_TD_SCDMA_LTE             = 15; /* TD-SCDMA and LTE */
int NETWORK_MODE_TD_SCDMA_GSM             = 16; /* TD-SCDMA and GSM */
int NETWORK_MODE_TD_SCDMA_GSM_LTE         = 17; /* TD-SCDMA,GSM and LTE */
int NETWORK_MODE_TD_SCDMA_GSM_WCDMA       = 18; /* TD-SCDMA, GSM/WCDMA */
int NETWORK_MODE_TD_SCDMA_WCDMA_LTE       = 19; /* TD-SCDMA, WCDMA and LTE */
int NETWORK_MODE_TD_SCDMA_GSM_WCDMA_LTE   = 20; /* TD-SCDMA, GSM/WCDMA and LTE */
int NETWORK_MODE_TD_SCDMA_CDMA_EVDO_GSM_WCDMA  = 21; /*TD-SCDMA,EvDo,CDMA,GSM/WCDMA*/
int NETWORK_MODE_TD_SCDMA_LTE_CDMA_EVDO_GSM_WCDMA = 22; /* TD-SCDMA/LTE/GSM/WCDMA, CDMA, and EvDo */

3.修改儲存，重啟，如果訊號不生效，就到 設定->應用->電話 清除快取即可