CMOS Checksum Bad: How Can Deal With It?

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Every time when I open the PC, the blue LED light flashes up, but it turned off after a second. Then suddenly, the LED flashes up again and then the message was displayed saying that the CMOS Checksum Bad. What does it mean? If it does continuously happen, how can I troubleshoot this problem?

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Answered By 563960 points N/A #194246

CMOS Checksum Bad: How Can Deal With It?

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The CMOS Checksum Bad error is a pretty common error that users often encounter just like me. Fortunately, this is an error that can easily be fixed so you don’t have to worry anything about. In my case, since I also fix computers, every time I encounter this error I often ignore it.

Because I know, it is a problem with the battery or the CMOS battery. I just fix the main issue on the computer first and just go back to the CMOS error when I’m finished where I only ask the owner to buy a new CMOS battery so I can replace the one installed on the motherboard.

And as soon as I installed a fresh battery, the CMOS Checksum Bad error disappears when booting. The error normally appears right after you turn on your CPU. Another possible cause of the error is a bad BIOS update or when a virus updated the BIOS. With my experience, I have never encountered a virus so strong that it managed to modify the BIOS information on the CPU.

The term checksum in the error message refers to the error detecting code that protects the BIOS settings or configurations that are stored in the CMOS memory. The error appears when the values don’t match. Since the checksum or the error detecting code that protects the BIOS configurations is stored in the CMOS memory, this value is verified against the stored value in the CMOS memory every time the computer boots.

When there is a mismatch on the values, the CMOS Checksum Bad error appears. If the values match, the computer boots normally. Also you will notice, when you have the CMOS Checksum Bad error, you will also see an error with the date and time saying it is not set. When you see this, it is an obvious indication that you have a weak CMOS battery. See image.

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