Have you noticed your Windows computer running slowly, with the disk usage constantly reaching 100%? When you open Task Manager to investigate the problem, you might find Diagnostic Policy Service consuming unusually high disk resources. In some cases, you may also notice a large diagnostic.log file taking up considerable storage space.
This issue can be frustrating, especially when you’re not running any demanding applications. Your computer may take longer to start, applications might freeze, and even simple tasks such as opening File Explorer can become noticeably slower.
The Diagnostic Policy Service (DPS) is a Windows service responsible for detecting, troubleshooting, and diagnosing problems with Windows components. It helps identify issues related to network connectivity, system performance, and other Windows functions.
However, if the service gets stuck, repeatedly generates diagnostic information, or encounters corrupted log files, it may cause excessive disk activity.
In this guide, I’ll explain how to fix Diagnostic Policy Service (diagnostic.log) high disk usage using several methods.
Why Is Diagnostic Policy Service Using So Much Disk?
The Diagnostic Policy Service (DPS) runs in the background and helps Windows identify and troubleshoot system problems. It collects diagnostic information and works with other Windows components to investigate issues.
Under normal circumstances, the service should not continuously consume excessive disk resources.
However, certain situations can cause unusually high disk activity. For example, a corrupted diagnostic log file may prevent the service from completing its operations properly. Similarly, repeated diagnostic requests, damaged system files, outdated Windows components, or problems with the storage drive can contribute to the issue.
The diagnostic.log file is associated with diagnostic activity. If it grows unusually large or is repeatedly accessed, it may contribute to excessive disk usage.
Now, let’s go through the solutions one by one.
Diagnostic Policy Service (diagnostic.log) High Disk Usage
If the Diagnostic Policy Service or diagnostic.log is consuming excessive disk resources, start by restarting the Diagnostic Policy Service, checking the diagnostic log file, and running Windows troubleshooting commands. You can also clear unnecessary diagnostic logs, repair corrupted system files, and check your drive for errors.
To resolve the issue, try these methods:
- Restart the Diagnostic Policy Service from the Services console.
- Clear the diagnostic log file and related temporary diagnostic data.
- Check Diagnostic Policy Service settings.
- Run the System File Checker and DISM scans.
- Use Disk Cleanup to remove unnecessary system files.
- Check your hard drive or SSD for file system errors.
- Install pending Windows updates.
- Perform a clean boot to identify conflicting applications.
1: Restart the Diagnostic Policy Service
The first solution is to restart the Diagnostic Policy Service. Sometimes, the service gets stuck while processing diagnostic information, causing continuous disk activity.
Restarting it can refresh the service and resolve temporary problems without changing your Windows configuration.
Press Windows + R to open the Run dialog box. Type services.msc and press Enter.
The Services window will appear, displaying the Windows services installed on your computer. Scroll down and locate Diagnostic Policy Service.
Right-click the service and select Restart, if the option is available.
If Restart is unavailable, select Stop, wait a few seconds, and then right-click the service again and select Start.
If Windows asks for administrator permission, approve the request.
Once the service starts again, open Task Manager > Processes and check the disk usage.
If the disk activity returns to normal, the problem may have been caused by a temporary service issue. However, if Diagnostic Policy Service continues consuming excessive resources, proceed to the next method.
2: Clear the Diagnostic Log File
A large or repeatedly accessed diagnostic log file can sometimes contribute to excessive disk activity.
Clearing unnecessary diagnostic logs may help resolve the problem, particularly when the service is repeatedly accessing problematic log data.
Before deleting anything, it’s important to understand that diagnostic logs can contain information useful for troubleshooting Windows problems. Therefore, avoid deleting unrelated system files.
Press Windows + R, type eventvwr.msc, and press Enter to open Event Viewer.
Navigate to Applications and Services Logs > Microsoft > Windows > Diagnosis-Scripted > Operational, if this log is available on your Windows installation.
You can review the recorded diagnostic events to identify repeated errors or unusual activity.
To clear this particular event log, right-click Operational and select Clear Log. Save the existing log if you want to retain it for troubleshooting.
You should also check the diagnostic.log file’s actual location before attempting to remove it. Open File Explorer and navigate to the folder containing the file, using the path identified through Task Manager or Resource Monitor.
If the file is actively being used by Windows, don’t force-delete it. First, investigate why it is growing and use the appropriate service or logging controls.
Important: Do not delete random files from the Windows or System32 folders. Removing essential system files can create additional problems.
After clearing the relevant log, restart your computer and check whether disk usage has improved.
3: Check Diagnostic Policy Service Startup Settings
Another thing worth checking is the startup configuration of the Diagnostic Policy Service.
If the service has an incorrect configuration or isn’t functioning as expected, Windows may encounter problems while performing diagnostic operations.
Press Windows + R, type services.msc, and press Enter.
Locate Diagnostic Policy Service, right-click it, and select Properties.
Under the General tab, check the Startup type option.
For most Windows installations, Diagnostic Policy Service should use Automatic startup.
If it is set to Disabled, change the startup type to Automatic. Click Apply and then OK.
Next, check the Service status. If it isn’t running, click Start, provided the option is available.
Restart your computer and monitor the disk usage again.
Avoid disabling this service permanently just to reduce disk activity. Doing so can interfere with Windows troubleshooting and diagnostic functionality.
4: Run DISM and System File Checker Scans
Corrupted Windows system files can sometimes interfere with Diagnostic Policy Service and other background services.
Fortunately, Windows provides two command-line utilities, DISM and System File Checker (SFC), that can help repair system corruption.
First, click the Start button and search for Command Prompt.
Right-click Command Prompt and select Run as administrator.
In the elevated Command Prompt window, enter the following command:
DISM /Online /Cleanup-Image /RestoreHealth
Press Enter and allow the scan to complete. DISM checks the Windows component store and attempts to repair detected corruption. Depending on your internet connection and computer performance, this process may take some time.
Once DISM finishes, enter the following command:
sfc /scannow
Press Enter and wait while Windows scans protected system files.
If SFC identifies corrupted files, it will attempt to replace them with healthy versions.
After both scans finish, restart your computer.
Open Task Manager and check whether Diagnostic Policy Service is still generating unusually high disk activity.
5: Run Disk Cleanup
If your computer has accumulated unnecessary temporary files, clearing them can help free up storage space and reduce storage-related pressure.
Windows Disk Cleanup provides a convenient way to remove several categories of unnecessary files.
Press Windows + R, type cleanmgr, and press Enter.
Select your Windows installation drive, usually C:, and click OK.
Wait while Windows calculates how much space you can recover.
Once the results appear, review the available categories, including Temporary files, Thumbnails, Delivery Optimization Files, and other unnecessary data.
Select the categories you want to remove and click OK > Delete Files.
If you want to remove additional system-related files, select Clean up system files and repeat the scanning process.
Be careful when selecting Downloads or Recycle Bin because these categories may contain files you still need.
After the cleanup finishes, restart Windows and check the disk activity.
Keep in mind that Disk Cleanup does not directly repair the Diagnostic Policy Service. It helps remove unnecessary files that may contribute to storage pressure.
6: Check Your Drive for Errors
Sometimes, high disk usage isn’t caused by Diagnostic Policy Service itself. Your storage drive may be experiencing file system errors or performance problems.
To check for these issues, you can use the CHKDSK utility.
Open Command Prompt as administrator and enter:
chkdsk C: /scan
Press Enter and allow Windows to scan the C: drive for file system errors.
This command performs an online scan without requiring you to immediately restart your computer.
If Windows reports errors that need repair, follow the recommended instructions. For offline repairs, you may need to run an appropriate CHKDSK repair command and restart your computer.
You can also check your drive’s health using your SSD or hard drive manufacturer’s diagnostic software.
If you notice unusual noises from a mechanical hard drive, frequent freezing, or repeated disk errors, back up important files as soon as possible.
A failing storage drive can cause high disk usage even when no application appears to be performing demanding operations.
7: Install Pending Windows Updates
An outdated Windows installation can sometimes contain bugs affecting system services and diagnostic components.
Microsoft regularly releases updates to improve system stability, security, and compatibility.
To check for updates, press Windows + I to open Settings.
Navigate to Windows Update and click Check for updates.
If updates are available, download and install them.
You should also check the Optional updates section under Windows Update > Advanced options > Optional updates.
If relevant driver updates are available, review them before installing.
Restart your computer after completing the updates.
Once Windows starts again, open Task Manager and check whether the Diagnostic Policy Service disk usage has returned to normal.
8: Perform a Clean Boot
If none of the previous methods resolves the problem, a third-party application or background service may be interfering with Windows diagnostic operations.
A clean boot helps identify such conflicts by starting Windows with a minimal set of drivers and startup programs.
Press Windows + R, type msconfig, and press Enter.
In the System Configuration window, select the Services tab.
Check the Hide all Microsoft services option first. This is important because disabling essential Microsoft services can affect Windows functionality.
Now, click Disable all to temporarily disable the remaining third-party services.
Next, open the Startup tab and select Open Task Manager.
Disable the enabled third-party startup applications one at a time or temporarily disable them all for testing.
Close Task Manager, click Apply, and select OK.
Restart your computer and check whether Diagnostic Policy Service is still causing high disk usage.
If the issue disappears, one of the disabled applications or services may be responsible. Re-enable the services and startup applications gradually to identify the problematic program.
Once you’ve completed the troubleshooting process, restore your normal startup configuration.
FAQs
1. What is Diagnostic Policy Service in Windows 11/10?
Diagnostic Policy Service is a Windows service responsible for detecting, diagnosing, and troubleshooting problems with Windows components. It helps identify issues involving network connectivity, system functionality, and other operating system features.
2. Is it safe to disable the Diagnostic Policy Service?
Disabling Diagnostic Policy Service is generally not recommended. It can interfere with Windows diagnostic and troubleshooting features. Instead, investigate why the service is consuming excessive resources and repair the underlying problem.
3. Why is diagnostic.log using 100% disk?
A diagnostic.log file may be repeatedly accessed or updated because of ongoing diagnostic activity, service problems, or repeated errors. However, 100% disk usage doesn’t automatically mean this file is responsible. Use Task Manager and Resource Monitor to identify the process and file generating the disk activity.
4. Can I delete diagnostic.log?
You should not delete the file without first identifying its exact location and purpose. Some diagnostic logs are safe to clear through their associated logging tools, but others may be actively used by Windows. Avoid manually removing system files.
5. How do I check which process is causing high disk usage?
Press Ctrl + Shift + Esc to open Task Manager. Select the Processes tab and click the Disk column to sort processes by disk activity. For more detailed information, open Resource Monitor by pressing Windows + R, typing resmon, and selecting the Disk tab.
6. Will restarting Diagnostic Policy Service fix high disk usage?
It can resolve temporary service-related problems, particularly when the service becomes stuck. However, if the underlying cause is corrupted system files, repeated diagnostic errors, or storage problems, additional troubleshooting may be necessary.
Final Words
The Diagnostic Policy Service (diagnostic.log) high disk usage problem can make your Windows 11/10 computer noticeably slower, particularly when disk activity remains unusually high for extended periods.
Fortunately, you don’t need to disable essential Windows services or reinstall your operating system to troubleshoot it.
Start by restarting Diagnostic Policy Service and checking the diagnostic logs. If the problem continues, run DISM and SFC scans, clear unnecessary temporary files, and check your storage drive for errors.
I’d recommend using Task Manager and Resource Monitor to identify the exact process and file responsible for the disk activity before deleting diagnostic data or changing service settings.