To check or start the Windows Modules Installer service, open services.msc and find Windows Modules Installer, or use its command-line service name, TrustedInstaller. A stopped service is not automatically a problem: Microsoft documents its startup type as Manual, so it may run only when Windows needs to service updates or optional components.
What the Windows Modules Installer service does
Windows Modules Installer is the display name for the TrustedInstaller service. Microsoft describes its role as enabling installation, modification, and removal of Windows updates and optional components. Starting it may be necessary for a servicing task, but does not by itself fix every Windows Update or system-file repair problem. Microsoft’s service guidance lists its startup type as Manual.
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Check its status and startup type
Use the Services console
- Press
Win+R, typeservices.msc, and press Enter. - Find Windows Modules Installer.
- Check the Status and Startup Type columns. A blank Status means the service is not currently running; Manual is consistent with Microsoft’s guidance.
Use PowerShell
Open PowerShell and run:
Get-Service -Name TrustedInstallerThis reports the service state. To inspect its start mode as well, run:
Get-CimInstance Win32_Service -Filter "Name='TrustedInstaller'" |
Select-Object Name, State, StartModeMicrosoft recommends checking a service’s startup type when a start request fails. For a simple visual check, Services is convenient; PowerShell is useful for repeatable checks or administration.
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Start the service
From Services
- In
services.msc, select Windows Modules Installer. - Select Start. If the service is already running, no start request is needed.
- Check the Status column again.
From an elevated PowerShell window
Run PowerShell as administrator, then enter:
Start-Service -Name TrustedInstallerStart-Service asks Windows Service Controller to start the service. If it is already running, the request is ignored without an error. Starting services generally requires elevation. Microsoft’s Start-Service documentation also notes that this cmdlet cannot start a service whose startup type is Disabled.
From an elevated Command Prompt
Open Command Prompt as administrator and run:
net start TrustedInstallerThis is a concise alternative for requesting a start. PowerShell offers a direct way to check state and inspect start mode; Services makes the current status and startup type visible together.
Quick Recap
If Windows Modules Installer will not start
- Check the exact name and start mode. The service name used in commands is
TrustedInstaller. If its startup type is Disabled,Start-Servicecannot start it. Microsoft documentsSet-Serviceas a way to change a disabled service’s startup type when appropriate. Do not override configuration on a managed device; ask its administrator if policy controls the setting. Microsoft’s PowerShell guidance explains this limitation. - Capture the full error. Note the complete message and your Windows version before choosing a repair. A failed start can have causes other than the startup type.
- Treat System Error 126 as version-specific. Microsoft’s documented registry repair for this error applies to Windows 7 SP1 and Windows Server 2008 R2 SP1. It involves reconstructing a Component Based Servicing registry value from servicing-stack folder names and changing permissions, so it is not a general fix for current Windows versions. See Microsoft’s System Error 126 article for the applicable systems and procedure.
- Diagnose update errors separately. Windows Update failures can have different causes; Microsoft identifies TrustedInstaller permissions in one specific error scenario. DISM is a built-in Windows servicing tool, but use it according to the relevant repair instructions for your Windows version and error rather than assuming a service start will resolve the issue. Microsoft’s Windows Update troubleshooting guidance and DISM repair guidance address those separate steps.
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