How to Fix a Cyclic Redundancy Check (CRC) Error

Sometimes, while you are using your computer, an error pops up that gets in the way of your work. One of them can stop you from copying files, accessing the data on your hard drive or even booting from it: the “cyclic redundancy check” error, or “data error (cyclic redundancy check)”.

Errors like this can have a logical or a physical cause, and repeated repair attempts can make things worse. If the files matter, see how professional data recovery works, starting with a free diagnosis.

If you have run into this problem and are looking for a solution, read on.

01What is a cyclic redundancy check?

A cyclic redundancy check (CRC) is a data verification method that computers use to detect errors on hard drives and optical discs (CDs and DVDs).

It is an error-detection technique widely used in digital networks and storage devices to catch accidental changes to raw data. When data is stored, a checksum is saved with it; when the data is read back, the checksum is recalculated. If the two don’t match, because a sector on the disk is damaged or the data was corrupted, you get a cyclic redundancy check error.

Let’s look at the main causes of this error.

02What causes CRC errors?

A CRC error can have several causes. Here are the most common ones.

Corrupted file and folder transfers

The CRC checks the integrity of the data being read, including the original files. If the source files and folders are already damaged, the error will appear when you try to copy or open them. So it is worth checking whether your source data is actually intact.

Problems with the storage device

External hard drives, for example, can develop faults such as bad sectors or failing heads. When that happens, the data can no longer be read reliably, the CRC check fails and Windows shows the error. If you get these errors on a brand-new drive the first time you use it, the device itself is the most likely culprit.

Connection problems

A poor connection between the computer and the storage device can also cause CRC errors. If you cannot copy or transfer data to or from the drive and keep getting error messages, check the cable, port and adapter you are using.

Viruses

Viruses can corrupt your files and folders and disrupt how the system works, which can lead to read and copy errors that look like CRC errors. It is always a good idea to make sure your computer is protected and to check whether it has been infected.

System crashes

As we mentioned, viruses can do a lot of damage to the system, but crashes and sudden shutdowns can also corrupt data. If the system crashes or loses power while data is being written or transferred, you may also end up with CRC errors. In that case, you will need to sort out the underlying system problem as well.

Buggy software

Some file transfer programs are poorly written and full of bugs, and they can corrupt data during the transfer. This alone can be enough to cause CRC errors.

03How to fix a cyclic redundancy check error

Now that you know what causes CRC errors, follow the steps below to fix the problem.

Scan the drive with CHKDSK

CHKDSK is a tool built into Windows that finds and repairs file system errors on disks. It can fix a number of minor errors and corrupted file system structures that may cause the cyclic redundancy check error. Important: a CRC error on a hard drive is often a sign of bad sectors. If the drive makes unusual noises, is very slow or holds data you cannot afford to lose, do not run CHKDSK: it forces the drive to read and write and can make the damage worse. In that case, switch it off and seek professional help.

To run it, follow these steps:

In File Explorer, right-click the drive you want to check, select “Properties” and open the “Tools” tab. Under “Error checking”, click “Check” (or “Check now” in older versions of Windows).

Please also note:

• If the error appears on a CD or DVD, it may be caused by scratches or dust. Clean the disc with a soft, clean cloth;
• Errors on optical discs usually cannot be repaired;
• If you see this error on a Mac (which is rarer), start by running the built-in Disk Utility and using “First Aid” on the drive.

Be prepared to wait for the scan to finish

In older versions of Windows, there are two scan options: a basic one, which fixes file system errors, and an advanced one, which also scans for bad sectors. Tick the box for the scan you want; the basic scan is the default.

The basic scan usually takes around 15 to 20 minutes, while the advanced one can take several hours. Make sure you have the time, and don’t use your computer until the scan is complete.

Restart your computer

If you are scanning the computer’s main hard drive (the one with the operating system), CHKDSK cannot run straight away. It will schedule the scan for the next time the computer starts, so you will need to restart to run it.

You can keep using the computer normally in the meantime and restart when you have time for the full scan.

If you suspect that the hard drive may be damaged, back up your important files before running the scan. Even if some data is inaccessible, save everything you can.

If you can’t run CHKDSK this way, use the command prompt

Sometimes running CHKDSK from the drive’s properties (as described above) doesn’t complete the scan or fix the errors properly. If that happens, run CHKDSK from the command prompt instead:

1. Press the Windows key, type “cmd” in the search box, right-click “Command Prompt” and select “Run as administrator”.
2. CHKDSK needs administrator privileges to run, so you must be signed in with an administrator account.
3. At the command prompt, type chkdsk x: /f, replacing “x” with the letter of the drive you want to check. For example, if it is drive C, type chkdsk c: /f and press Enter.
4. This command runs the basic scan. To run the advanced scan, which also looks for bad sectors, type chkdsk x: /r, again replacing “x” with the drive letter. Only use /r on a drive that is physically healthy and whose data is already backed up.
5. Wait for the scan to finish. When it is done, CHKDSK will show a report (and, if it scanned the system drive, restart the computer). If the errors have been fixed, you’re all set.
6. If the /r scan seems to freeze or never finishes (even after hours), the drive most likely has physical damage that CHKDSK cannot repair. Stop the scan, switch the drive off and don’t try again: every extra attempt stresses the drive and can make the data harder to recover.
7. Over time, a hard drive can develop minor file corruption and other errors. CHKDSK can fix many small problems, but not the most serious ones, and never physical faults.

04Conclusion

Disk problems can’t always be fixed with simple tools, especially when the problem is serious. The most important thing is to get into the habit of backing up the data you can’t afford to lose, and keeping more than one backup is best practice.

If you have tried these tips and your drive still has problems, don’t despair. Get in touch with the Bot team and we’ll give you the help you need.

We also offer free collection of your device (islands not included) and a free standard diagnosis.

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