OSError: fusion hat driver not loaded

General
1

I’ve been doing Paul’s courses without issue for the first 8 courses. When I turned the pi-5 on and started the 9th, I get an OSError, fusion hat driver not loaded.

I have already re-flashed my SD with V1.0.0 with the same results. Other issues are the homework assignments from prior will not work and give the same error. I am also missing the orange charge LED on the hat now. I did not update, and this second copy doesn’t even give me the icon on the taskbar.

I’ve searched other posts similar and they seem to abruptly end without revealing the issue.

running fusion hat doctor fails I2C MCU(0x17) sysfs interface.

Did my hat go belly up?

2

OK, little odd but I held the pwr and USR buttons and I now have the orange LED illuminated, so I tried 'fusion_hat enable_speaker" and it accepted it without problem. I tried “fusion_hat test_speaker” and it ran just as it was supposed to.

I would try running my homework programs, but alas, they are history because of the reflash.

I modify my issue to : What happened to turn my orange LED off?

3

Thank you for your post and the troubleshooting steps you tried.

Initially, we suspected a faulty HAT, a driver issue, or an EEPROM problem. However, we noticed that pressing the PWR and USR buttons temporarily resolved it — which is interesting, since we have no software configuration for those buttons.

This brings up a simple (perhaps even silly) question: Could your Fusion HAT have been without power or not fully booted up, causing the orange LED to stay off? The button press might have acted as a hardware reset or wake-up signal.

If possible, could you try power-cycling your Pi to see if the issue returns, and then test the button combination again? Your feedback would help us confirm this.

4

Here are our thoughts on the points you raised:

About the orange LED disappearing – This sounds like an unexpected power loss. The orange light is the power indicator; it should stay on whenever the HAT is connected to a power source and turned on. One possibility is that the battery connector became loose, and your action of pressing the PWR button may have accidentally re-seated it, restoring the connection.

About “this second copy doesn’t even give me the icon on the taskbar” – We’re not entirely sure what you mean by this. Could you please send us a photo showing what you see? That would help us understand better.

About the “OSError: fusion hat driver not loaded” – This sounds like the Raspberry Pi booted up, but the Fusion HAT did not receive power. May we ask: are you powering the Pi separately via its own USB-C port? Our recommended setup is to power the Fusion HAT directly via its power input (or use the battery alone), and let the HAT supply power to the Pi – there is no need to power the Pi separately.

We look forward to your reply and any photos you can share. Please feel free to test the power connection and let us know the results.

5

I’ve tried several times without any issues. I am using a 45W power pack connected to the hat. when I shut down the pi, the hat stays powered. I have a red light on the pi, and have to hold the pwr button on the hat, which rapidly flashes the orange lights then the green light goes out, but the orange stays on.

During the issue, the orange LED only would flash a couple times as the pwr button was held, but the as soon as the power button was released the green pwr led would come back on, the pi would boot, but the orange light would never illuminate at all. I had to unplug power to turn it off.

6

I had no mains electric power loss, the batt connecter is pretty tight and in. I had disassembled the stack and reassembled ,including unplugging and replugging the battery. In order to turn the power off (green led on the hat) I had to remove the 45W input AND the battery to turn it off. This was done several times as I was reseating and trying some of the recommendations on other posts (enable_speaker, doctor etc)

The icon I talked is for updating, and it is now present in the taskbar. I never pressed to update at any time, but I thought about it to see if there was any change since I already had a new OS flash (V1.0.0).

The pi has no power to it. The hat has 2 sources, the batteries and the 45W input. The 45W input was purchased with the pi at the same time as the fusion hat kit, which is about 7 days old. Not saying the power supply isn’t faulty because it’s new, just saying there have been no other indications of it. The only other issue I had was the pi looking for a login at bootup just once, which happened maybe the 12th time turning it on. It wouldn’t accept any password, and the solution turned out to be just turn it off and back on. I haven’t seen it since, and that would have been with the first OS flash.

7

Sorry I couldn’t get it to reproduce. If there is an issue with this particular hat I’m sure it will happen again. I will return to this thread without doing anything to my pi or hat in order for you to get a whack at finding the issue.

8

Thank you for your detailed testing and documentation—this is very helpful for our troubleshooting.

Regarding your question about why the orange LED turned off, here is our analysis:

  1. The orange LED is controlled by the power management MCU

The orange LED is the power/charging indicator on the Fusion HAT. It is managed by the onboard power management MCU (the same chip at I2C address 0x17 that fusion_hat doctor was trying to access). This MCU handles power switching between the 45W adapter and the battery, as well as LED status control.

  1. A power-switching logic glitch may have caused the MCU to hang

When both the 45W adapter and the battery are connected simultaneously, the MCU needs to complete its initialization sequence to properly manage the power sources. Under certain conditions—such as plugging/unplugging the battery, rapid power on/off cycles, or momentary voltage fluctuations from the adapter—the MCU can get stuck in an intermediate state. In this state, it is neither fully off nor fully on:

The green standby LED stays on (so the Pi can boot).

The orange main power LED does not illuminate.

The I2C interface becomes unresponsive, which is why fusion_hat doctor reported an I2C MCU error and the driver failed to load.

  1. Pressing PWR + USR performs a hardware reset on the MCU

Your action of holding down both the PWR and USR buttons likely triggered a forced hardware reset on the MCU, causing it to restart its boot sequence properly. This is why:

The orange LED came back on.

enable_speaker and test_speaker started working again.

Since everything returned to normal afterward, this does not appear to be a permanent hardware failure. It is more consistent with a one-time power management state anomaly.

  1. The login screen issue and taskbar icon are unrelated to HAT hardware

The occasional login screen freeze you encountered is most likely related to the SD card filesystem experiencing a minor hiccup during boot (possibly due to an improper shutdown or power transition). A simple reboot resolved it, which confirms it was not HAT-related.

The taskbar icon reappearing later is a normal sign that the system successfully detected the HAT after the MCU recovered. Its earlier absence was probably because the HAT was not fully ready at boot time.

Recommendations moving forward:

Since the HAT is now working normally, you can safely continue with your coursework.

If the orange LED fails to illuminate again in the future, try the PWR + USR button combination first as a quick reset—there is no need to immediately re-flash the SD card.

If the issue becomes frequent, consider testing with only the battery (without the 45W adapter connected) for a period of time to rule out any instability from the power adapter, even though it is new.

Please feel free to return to this thread if the issue reappears—we will continue to assist you. Thank you for your patience and understanding!