Unbrick Redmi Note 4 (MediaTek) Bootloop with cust.img: SP Flash Tool Guide

Updated November 2026. Short answer: if a MediaTek Redmi Note 4 (codename nikel) is stuck in a bootloop after you flashed another region’s ROM, reflash the China Fastboot ROM with SP Flash Tool, replacing its cust.img with an empty or global one. The cust partition holds region-specific apps and settings, and a mismatched one is the most common cause of this bootloop. Your IMEI and modem stay untouched.

Check your model first. This guide is only for the MediaTek Redmi Note 4 (Helio X20, sold mainly in China). The Redmi Note 4 sold in India and globally, and the Redmi Note 4X, use a Snapdragon 625 (codename mido) and are flashed with Mi Flash instead. See the Redmi Note 4 / 4X (mido) firmware page. In Fastboot mode, fastboot getvar product shows the codename.

What you need

• The latest China Fastboot ROM for nikel (MIUI 10, V10.2.2.0.MBFCNXM) from our Redmi Note 4 MediaTek firmware page. It links straight to Xiaomi’s servers.
• SP Flash Tool and the MediaTek VCOM driver: see MTK driver and SP Flash Tool for Redmi Note 4.
• One of the replacement files:
  • cust.rar: an empty cust.img (about 6 KB). It removes all region apps and is the safest fix.
  • cust_global.rar: a global cust.img (2.9 MB) with English apps and settings instead of the China ones.
• A Windows PC, a good USB cable and at least 50% battery.

Method 1: Flash with an empty cust.img

1. Extract the China Fastboot ROM (.tgz) with 7-Zip and open the images folder.
2. Extract cust.rar and replace the original cust.img (about 500 MB) with the new one.
3. Open SP Flash Tool. As Download-Agent choose MTK_AllInOne_DA.bin from the SP Flash Tool folder. As Scatter-loading file choose MT6797_Android_scatter.txt from the images folder.
4. Keep the mode on Download Only and click Download.
5. Turn the phone off, then connect it to the PC while holding Volume Down. The flash starts automatically.
6. Wait for the green “Download OK” circle, disconnect the phone and turn it on. The first boot takes several minutes.

Method 2: Flash with the global cust.img

Same steps, but use the 2.9 MB file from cust_global.rar, and in SP Flash Tool untick “preloader” in the partition list before you click Download. Keeping the existing preloader avoids problems if the download is interrupted.

If SP Flash Tool shows an error

• BROM ERROR: S_BROM_CMD_STARTCMD_FAIL or nothing happens: reinstall the MediaTek VCOM driver and try another USB port (USB 2.0 works best) and another cable.
• STATUS_SEC_AUTH_FILE_NEEDED or an “authorized account” prompt: newer Xiaomi bootloaders require an authorized Mi account for SP Flash Tool. Most original Redmi Note 4 builds don’t. If yours does, community tools such as mtkclient can bypass the check on this chip, at your own risk.
• PMT changed error: switch to Firmware Upgrade mode once. It rewrites the partition table, so all data is erased.

FAQ

What is cust.img?

It’s the image of the cust partition: region-specific apps, language packs and settings that MIUI loads at boot. A cust partition from a different region can make the phone loop on the MI logo, even though the system partition itself is fine.

Will this erase my data?

“Download Only” with a full Fastboot ROM overwrites the system and usually user data too. Back up first if the phone still boots to recovery. IMEI and modem calibration are not touched in Download Only mode.

Can I install a Global ROM on the MediaTek Redmi Note 4?

Yes. Xiaomi released an official Global Fastboot ROM for nikel, the last one is V10.2.1.0.MBFMIXM (MIUI 10), on our firmware page. Flash it the same way with SP Flash Tool. If the phone then loops, use the cust.img fix above with that ROM.