STATUS_TIMER_RESUME_IGNORED (0X40000025) Fix: Why Your Timer Flag Got Ignored

You're working on a PC that's been acting flaky — maybe a custom app, a driver, or some piece of industrial software. Every time the machine wakes from sleep, you see this in the Event Viewer under System logs: STATUS_TIMER_RESUME_IGNORED (0X40000025). It's not a crash, not a BSOD, just a warning. But if you're seeing it over and over, something's off.

What triggers this error?

I see this most often in two scenarios: First, a custom-written timer in a driver or app that calls KeSetTimerEx or SetWaitableTimer with a resume flag set — but the system ignores it because the timer's already expired or the PC's power state changed. Second, it happens with legacy hardware or drivers that don't handle modern sleep states (S3, Modern Standby) properly. Had a client last month whose manufacturing floor software threw this warning every morning after the PC woke from sleep. The app was polling a serial port with a timer that assumed the system never slept.

Root cause in plain English

Windows timers have a flag called TIMER_RESUME or WT_SET_RESUME. You set it to tell the system 'hey, when this timer fires, wake up the CPU if it's sleeping.' But Windows has rules: if the timer's already overdue (expired while the PC was asleep), or if the system's power state doesn't allow resuming (like in Modern Standby with certain drivers), it just ignores the flag and fires the timer normally. The error code is informational — it's saying 'I saw your flag, but I'm not using it.' It's not a bug, it's a design choice. But it can indicate a misbehaving timer that should be re-armed differently.

The fix: three steps

Skip the registry dives and random driver updates. Here's what actually works.

Step 1: Identify the offender

Open Event Viewer (eventvwr.msc). Go to Windows Logs > System. Filter by event ID 0x40000025. Look at the source. If it says Kernel-General or a specific driver name (like serial.sys or usbuhci), that's your hint. If it's a custom app, check the app's logs or contact the vendor. For example, the client's app was logging Timer: 0x40000025 from windows_timer.cpp:145 — that's a clear pointer.

Step 2: Adjust the timer re-arm pattern

If you're writing code, don't set the resume flag on a periodic timer that doesn't need to wake the system. Use WT_SET_RESUME only for critical timers (like a wake alarm). For non-critical timers, just set the expiration without the flag. In kernel mode, don't call KeSetTimerEx with the DueTime in the past — that's a common mistake. The fix is to check KeQuerySystemTime before setting the timer:

// Bad: timer set with resume flag, but due time is in the past
KeSetTimerEx(&timer, dueTime, period, &dpc); // ignores resume flag

// Good: check if the due time has already passed
if (dueTime.QuadPart > KeQueryInterruptTime().QuadPart) {
    KeSetTimerEx(&timer, dueTime, period, &dpc);
} else {
    // handle immediately, don't set timer
    DpcRoutine(&dpc, NULL, NULL);
}

Step 3: Update or replace the problematic driver/firmware

If the source is a driver like serial.sys, usbhub.sys, or something from a third-party vendor, go to the hardware manufacturer's site and get the latest driver. I've seen this fixed by updating chipset drivers or disabling 'Allow the computer to turn off this device to save power' in Device Manager for the suspect hardware. If it's a custom app, ask the vendor to use SetWaitableTimer with the CREATE_WAITABLE_TIMER_HIGH_RESOLUTION flag instead — it handles resume better on modern Windows (10/11 21H2+).

What to check if it still fails

If you've done all that and the warning still appears, check your power plan. On Windows 10/11, go to Control Panel > Power Options > Change plan settings > Change advanced power settings. Under Sleep, set 'Allow hybrid sleep' to Off. Under PCI Express, set 'Link State Power Management' to Off. That's overkill, but it stops Modern Standby's aggressive state changes that confuse old timers. Also check if the system's using S0 (Modern Standby) instead of S3 — run powercfg /a in an admin command prompt. If it says 'S0 Low Power Idle' supported, try disabling it in BIOS (look for 'Deep Sleep' or 'S3 Support').

One more thing: if you're debugging a kernel driver, use !analyze -v in WinDbg on a crash dump that includes this warning — it'll show the timer's due time and the current system time. Nine times out of ten, the due time's in the past. Fix that, and the warning disappears.