CMOS Checksum invalid on HP Spectre x360 13-ap0317ng

[FabianBa]

Hello everyone,

I'm having an issue with my HP Spectre x360 13-ap0317ng: The battery was pretty dead, so I replaced it with a new one. Since original HP replacement batteries are no longer available, I had to use a third-party battery. I double-checked all values as thoroughly as possible to ensure compatibility.

After replacing the battery, I am now greeted with the following error message:

No matter what key I press, I keep looping back to this screen and can't proceed any further. Switching back to the old battery I am greeted with the same screen (I need to have the charging cable in all the time when using the old battery).

I already considered removing the CMOS battery to reset the BIOS, but it seems to be bundled with the main battery. Other than that, I have not changed anything on the motherboard or its connections, and there are no visible physical damages.

Here’s what I have checked so far:
✅ The SSD is working, as it is detected when installed in another PC (though Bitlocker prevents me from getting more details).
✅ The LED blinks white a few times when restarting.
✅ I have not attempted a BIOS update or recovery from a USB stick, as I don’t have a recovery medium available.

I have plenty of experience with hardware, having built over 20 PCs myself, and I’ve always been able to solve issues – but this time, I’m stuck.

Does anyone have an idea how to get out of this loop? What would be the best next step?

Thanks for any helpful input!
Best regards 🙂

[Garp_senchau]

@FabianBa, Welcome to HP Support Community,

Thank you for posting your query; I’m here to help by guiding you through steps to resolve this issue

CMOS Reset (502) The CMOS checksum is invalid

During the startup process, the system performs a checksum test of the BIOS. If the checksum is incorrect, the BIOS is assumed to be corrupt and the system installs a hidden copy of the BIOS to correct the problem, and the startup process continues. The following message displays for 15 seconds before the computer automatically reboots. You have the option of pressing enter to proceed without waiting 15 seconds.

To resolve the CMOS Reset Error (502), restore the BIOS.

Press enter to restart the PC.

If the error displays after restarting, try to restore the BIOS using a USB drive. For more information, see the "Recover the BIOS using a USB recovery drive" section of the following:

• For desktop computers, go to HP Desktop PCs - Recovering the BIOS (Basic Input Output System).
• For notebook computers, go to HP Notebook PCs - Recovering the BIOS (Basic Input Output System).

Reference: HP PCs - 500, 501, or 502 error displays on a black screen | HP® Support

I hope these steps help resolve the issue

Please feel free to reply here if you have any questions or if you need further clarification on any of the steps. 

Take care and have a good day. 

If my response helped you or made things easier, I’d truly appreciate it if you could mark it as an Accepted Solution! ✅ This not only helps others find the right fix faster but also spreads the support. 💙 And if you found my reply helpful, tapping "Yes" on "Was this reply helpful?" means the world- it ensures more people get the solution they need! 🌟 Your small action can make a big impact! 💪😊

Regards,

[FabianBa]

@Garp_senchau: Thank you for your reply.

I followed your instructions. However, only the Win+B method worked to reset the BIOS during startup. The USB stick method did not work.

After restarting the system following the BIOS recovery, I was greeted once again by the CMOS Reset (502) screen. I repeated this process twice yesterday, but without making any real progress.

Today, I tried to start the laptop again, initially by simply pressing the power button as usual. Once again, the 502-CMOS screen appeared. When I press Enter, the screen turns off, and the LED on the power adapter starts blinking white: it lights up briefly, then stays off for a moment, and repeats this pattern continuously.

After unplugging the power adapter, the blinking stopped. When I plugged it back in, it started again. So, I opened the device and disconnected the battery to break the loop. Before reconnecting it, I held the power button for 30 seconds twice to fully discharge the system.

Then, I reset the BIOS again. This time, the laptop turned off completely, and the LED remained off, even though the power adapter was plugged in. If I unplug and reconnect it, the LED flashes white once, then stays off.

I disconnected the battery again, discharged the system, and reconnected it. After booting, the 502-CMOS screen appears again.

Unfortunately, I'm still stuck. 😞

[Garp_senchau]

@FabianBa,

Unfortunately, it seems there are no other steps we can perform to resolve this issue. At this point, the device will need to be repaired. I recommend taking the unit to the nearest HP authorized service station for further assistance. I will also send you the details to contact our team via private message to help you with the next steps.

To access your private message, just click the little blue envelope icon on the upper right corner of your HP Community profile, next to your profile name. Alternatively, you can click on this link. 

We're looking forward to helping you resolve this issue! 

Stay tuned, and thanks for your patience! 

Regards,