The dead end: no error, just nothing

The Super I/O chip on these Tiny-series boards is a Nuvoton NCT6683, and the matching kernel driver is nct6683 (part of lm-sensors). Normally you modprobe nct6683, run sensors-detect, and get fan1/fan2 readings for free. Here, modprobe nct6683 returned cleanly, but sensors still showed no fan entry:

modprobe nct6683
sensors
# coretemp-isa-0000 and peci entries present, no nct6683 block at all
dmesg | grep -i nct6683
# (nothing)

No error message, no log line, nothing in dmesg — the module just wasn’t registering a device. That absence of any error is the tell: this isn’t a missing-driver problem, it’s a driver that loaded and then quietly declined to attach to the hardware.

The cause: an EC firmware/vendor check

The nct6683 driver does a sanity check against the embedded controller’s firmware build ID before it will bind — it’s a safety measure, since writing to the wrong registers on an unrecognized EC build can do bad things. This M900 Tiny’s EC firmware build (1.0 build 12/30/15) isn’t in the driver’s list of known-good builds, so the check fails and the driver bails out with ENODEV before ever creating the sensor device — silently, since this is treated as “unsupported hardware,” not an error condition.

The driver exposes an escape hatch for exactly this: a force module parameter that skips the vendor/build check and binds anyway.

modprobe -r nct6683
modprobe nct6683 force=1
sensors

With force=1, sensors immediately reports a new block with fan2 reading a baseline of roughly 980 RPM, alongside the existing coretemp/PECI entries.

Making it persistent

A manual modprobe force=1 doesn’t survive a reboot, and doesn’t help if nct6683 isn’t in the auto-loaded module list at all. Two small config files fix both:

# Force the parameter every time the module loads
echo "options nct6683 force=1" > /etc/modprobe.d/nct6683.conf

# Make sure the module actually loads at boot
echo "nct6683" >> /etc/modules

update-initramfs -u
reboot

After the reboot, sensors shows fan2 without any manual intervention — same as it would if the driver’s built-in check had recognized the board in the first place.

Reference

If a Super I/O sensor driver loads without error but produces zero fan/temp entries and dmesg is silent, a vendor or firmware-build allowlist check inside the driver — not a missing driver — is worth suspecting before anything else.

This guide was written by Claude, an AI assistant made by Anthropic, based on a hands-on troubleshooting session working through this exact problem.