Comprehensive Guide: Rooting Oppo A18 (CPH2591) and Installing TWRP/GSI ROMs

This guide provides a detailed walkthrough for rooting your Oppo A18 (CPH2591) device, installing a custom recovery such as TWRP (if available), and flashing a GSI ROM like Evolution X. This process is advanced and requires careful attention to detail. A mistake can potentially brick your device. Proceed with caution and only if you understand the risks. This guide assumes a basic understanding of ADB, Fastboot, and flashing processes. Since your bootloader is locked and Fastboot isn’t working, we’ll explore alternative methods. We will also outline potential workarounds and troubleshooting steps based on your provided details.

Prerequisites and Warnings

• Backup Your Data: Before proceeding, back up all important data from your Oppo A18. This process may wipe your device.
• Battery Charge: Ensure your phone has at least 60% battery charge to prevent interruptions during the process.
• Oppo Drivers: Install the necessary Oppo USB drivers on your computer. This is crucial for device recognition during ADB and other processes. You can usually find them on Oppo’s official website or through driver installer tools.
• ADB and Fastboot: Install the latest version of ADB (Android Debug Bridge) and Fastboot tools on your computer. Ensure they are correctly configured and accessible from your command line.
• Stock ROM: You already have the full stock ROM, including boot.img, recovery.img, and scatter.txt. This is crucial for restoration if something goes wrong. Keep these files safe.
• Understanding the Risks: Rooting, flashing custom recoveries, and installing GSI ROMs are inherently risky. You could potentially brick your device (render it unusable). We are not responsible for any damage to your device.
• Warranty Void: Proceeding with these steps will likely void your device’s warranty.

Step 1: Obtaining Necessary Tools and Files

• MTK Drivers: Even though MTKClient isn’t detecting your phone yet, download and install the MediaTek USB drivers. Sometimes, a fresh installation or different versions can resolve detection issues.
• SP Flash Tool: Download the latest version of SP Flash Tool. Although you’ve encountered “DA mismatch” errors, we’ll try different DA files and configurations later.
• DA (Download Agent) and Auth Files: This is where the “DA mismatch” error comes into play. DA files are specific to the chipset. Since you have an MT6768 (Helio G85), try to source DA files specifically for this chipset. XDA Developers forums and other Android development communities are good resources. You might also need an “Auth” file, which is required to bypass secure boot on some devices. Finding a working Auth file can be challenging and often requires research.
• Magisk Patched Boot Image: You’ve already patched boot_a.img with Magisk. This is good. Keep this file readily available.
• TWRP (if available) or Alternative Recovery: Since you haven’t found a reliable TWRP image for the A18, keep looking, but be extremely cautious. Generic images are often unsafe. Consider looking into OrangeFox Recovery as an alternative, tailored for MediaTek devices.
• GSI ROM (Evolution X): Download the ARM64 A/B version of Evolution X (or your preferred Pixel-based GSI ROM). Make sure it is compatible with your device’s architecture.

Step 2: Addressing BROM and Fastboot Issues

Since standard Fastboot commands are not working, and you cannot reliably access BROM mode, this presents a significant hurdle. We’ll need to focus on alternative methods:

2.1. Troubleshooting MTKClient and BROM Access

• Driver Issues: The primary reason MTKClient might not detect your phone is driver-related.
  • Disable Driver Signature Enforcement: On Windows, disable driver signature enforcement. This allows unsigned drivers to be installed. Search online for guides on how to do this, as the method varies slightly between Windows versions.
  • Test Different USB Ports and Cables: Use a high-quality USB cable and try different USB ports on your computer (preferably USB 2.0 ports).
  • Manual Driver Installation: In Device Manager, manually locate and install the MediaTek Preloader USB VCOM port driver when your phone is connected in what should be BROM mode. Sometimes Windows fails to automatically install the correct driver.
• Forcing BROM Mode (Advanced):
  • Disassembly (Last Resort): As a last resort, if you’re comfortable with hardware, you might be able to access BROM mode by shorting specific test points on the motherboard. This is extremely risky and can permanently damage your device. Only attempt this if you have experience with electronics repair and are willing to accept the risk. Search for the Oppo A18’s PCB diagram to identify potential test points for BROM access.
  • Crash Preloader (Alternative): You mentioned trying the “Crash Preloader to BROM” trick. This usually involves sending a specific command or flashing a corrupted preloader to force the device into BROM mode. However, the specific method varies depending on the device and chipset. Research specific techniques for MT6768 devices.
• MTKClient Command-Line Options: Explore different MTKClient command-line options. Sometimes, specific commands can bypass the initial detection issues. Refer to the MTKClient documentation for a complete list of commands.

2.2. SP Flash Tool Adjustments

• DA and Auth File Selection: In SP Flash Tool, carefully select the correct DA file for your MT6768 chipset. Try different DA files specifically designed for the Helio G85. If you have an Auth file, load it in the SP Flash Tool’s “Authentication File” section.
• Download Agent Configuration: Some DA files require specific configurations within SP Flash Tool. Consult the documentation or forums where you obtained the DA file for any special instructions.
• Scatter File Loading: Load the scatter.txt file from your stock ROM into SP Flash Tool.
• Preloader Flashing (Caution): Only attempt to flash the preloader if you are absolutely sure you have the correct preloader file for your device and chipset. Flashing an incorrect preloader will almost certainly brick your device.

Step 3: Unlocking the Bootloader (If Possible)

Since you mentioned the bootloader appears to be locked with no obvious way to unlock, this is a major problem. Most modern Android devices require an unlocked bootloader to flash custom recoveries and ROMs. Without an unlocked bootloader, you will be severely limited in what you can do.

• Oppo Developer Options and OEM Unlocking: Check if “OEM Unlocking” is present and enabled in Developer Options. If it’s not present, it means Oppo has likely disabled this option for your device’s specific firmware.
• Hidden Unlock Codes: Some Oppo devices have hidden unlock codes or methods. Research online for specific unlock methods for the Oppo A18 (CPH2591). XDA Developers and other Android forums might have information.
• Paid Unlock Services (Use with Extreme Caution): As a last resort, there are paid services that claim to unlock bootloaders on devices that officially don’t support it. However, these services are often unreliable, expensive, and potentially dangerous. Use them with extreme caution and only if you are willing to risk your device and your money.

If you cannot unlock the bootloader, you will likely be unable to flash TWRP or a GSI ROM. Rooting might still be possible via Magisk patching, but flashing a custom recovery or ROM will likely be out of reach.

Step 4: Rooting via Magisk (If Bootloader is Still Locked)

Even if the bootloader remains locked, you can still attempt to root your device using the Magisk-patched boot image you created. This will grant you root access without needing to flash a custom recovery.

• Flashing the Patched Boot Image (SP Flash Tool):
  1. Open SP Flash Tool.
  2. Load the scatter.txt file.
  3. Locate the “boot” partition in SP Flash Tool.
  4. Select the boot_a.img (the Magisk-patched boot image) for the boot partition.
  5. Ensure that you are flashing to the correct partition (boot_a in your case).
  6. Flash the image.
• Verifying Root: After flashing, reboot your device. Install the Magisk Manager app. If Magisk Manager shows that Magisk is installed, your device is successfully rooted.

Step 5: Installing TWRP or OrangeFox (If Bootloader is Unlocked)

This step is only possible if you have successfully unlocked the bootloader.

• Flashing via Fastboot:
  1. Download the TWRP or OrangeFox image for your device (if available).
  2. Reboot your device into Fastboot mode (if you have somehow enabled it).
  3. Open a command prompt or terminal on your computer.
  4. Type the following command: fastboot flash recovery <recovery_image.img> (replace <recovery_image.img> with the actual name of the recovery image file).
  5. Type: fastboot reboot
  6. Immediately press the key combination to boot into recovery mode (usually Volume Up + Power button, but it might be different for your device).
• Flashing via SP Flash Tool (Alternative): If Fastboot is still not working but you have a working BROM connection, you can flash the recovery image using SP Flash Tool, similar to how you would flash the boot image.

Step 6: Flashing a GSI ROM (If TWRP/OrangeFox is Installed)

This step is only possible if you have successfully unlocked the bootloader and installed TWRP or OrangeFox.

• Backup (Important): In TWRP or OrangeFox, create a full backup of your current system. This will allow you to restore your device if something goes wrong.
• Wipe Data: Wipe the system, data, and cache partitions. This is crucial for a clean installation of the GSI ROM.
• Flash GSI ROM: Select “Install” in TWRP/OrangeFox and locate the GSI ROM image file. Flash the image.
• Flash GApps (Optional): If the GSI ROM doesn’t include Google Apps (GApps), flash a GApps package (e.g., NikGApps, Open GApps). Choose the ARM64 version.
• Reboot: Reboot your device. The first boot may take a while.

Step 7: Troubleshooting and Post-Installation Steps

• Boot Loops: If your device gets stuck in a boot loop after flashing the GSI ROM, try wiping the cache and Dalvik cache in TWRP/OrangeFox.
• No Network: If you have no network connectivity after flashing the GSI ROM, you might need to flash a modem file or configure APN settings.
• Camera Issues: Camera issues are common with GSI ROMs. You might need to find a compatible camera module or use a different GSI ROM.
• Fingerprint Sensor: Fingerprint sensor compatibility varies between GSI ROMs. You might need to experiment with different ROMs to find one that works correctly.
• VoLTE/VoWiFi: VoLTE and VoWiFi support are also dependent on the GSI ROM and your carrier. You might need to configure specific settings or flash additional files.

Disclaimer

This is a complex process, and there’s no guarantee of success. Each device is different, and the steps may vary. Always research thoroughly and proceed with caution. If you’re unsure about any step, seek help from experienced users in Android development communities like XDA Developers. We are not responsible for any damage to your device.