Fixing Windows CMOS Checksum Error (Solved)

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The CMOS contains BIOS-related data and may have been reset, causing this error. The problem could also be caused by draining the CMOS battery. If a CMOS checksum error occurs at system startup, it may indicate that the system has been reset to the factory default settings.

Each time you perform a BIOS update, start or shut down your computer, these events are recorded in the CMOS. It keeps a record of these things to make sure they work normally the next time you start your computer. The CMOS remains on while the rest of the computer is off because it operates independently of a clock battery. When the computer starts, it tries to read the last state it was in on the CMOS. Normally, he can read the information and recover without any problem. A CMOS checksum error occurs when the computer cannot read this information or it does not match completely.

How to Fix CMOS Checksum Error on Windows

Resetting the BIOS defaults


  • Start the computer on the black screen with the checksum error.
  • If you see the message “Press F1 to continue, F2 to enter SETUP”, press F2 to enter the BIOS. (You may need to press other keys, such as the Delete key, depending on the BIOS).
  • Read the information on how to use the keys on the screen and select the Load Defaults option. Or select the option that works for the default BIOS setting.

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  • When the system gives the command “Load BIOS Defaults (Y/N)”, press the Y and Enter keys.
  • After entering Windows, turn off the computer and restart it to see if the problem persists.
  • Save the changes and exit the BIOS.

Replace the CMOS battery

  1. Open the computer case and find the CMOS battery that is connected to the motherboard of your computer. If you cannot find your CMOS battery, refer to the documentation on your motherboard or computer. You can also consult it on the Internet or ask the manufacturer of your computer for help.
  2. If your computer uses a button cell battery, it is relatively easy to remove the battery. Grasp the edge of the battery with your fingers and pull it up and out of the grip that holds it. Some motherboards have a clip that holds the battery in place, and you may need to lift it up to remove it.
  3. Keep it removed for 10 minutes, take the other one, type it in the same way and try to start your computer. Check if the CMOS checksum error is displayed!

Fix the CMOS battery’s terminals

A problem people face is the error message that continues to appear even after the CMOS battery has been replaced. Normally, if the battery has more than 3 volts, the CMOS should operate correctly and reset the BIOS settings.

This could still be a power problem, but not the battery itself. On the contrary, the negative and positive pins that draw energy from the battery may not be properly connected. The battery would therefore be loose and would not provide energy.

Remove the battery and fold the negative pin and also fold the positive pin, or anything that ensures that both pins have firm contact with the battery. Then replace the battery and check that it is tightened when both terminals are properly connected. Put everything back in place and restart the machine.

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