Unable to use when pwm1_enable file is not readable

[oldherl]

On my system (Dell Latitude laptop), the file /sys/class/hwmon/hwmon3/pwm1_enable is not readable, even for root.
But it is writable and /sys/class/hwmon/hwmon3/pwm1 is both readable and writable.

thinkfan exits with error message Initializing fan control in /sys/class/hwmon/hwmon3/pwm1: Permission denied

If I manually write 0 or 128 or 255 into /sys/class/hwmon/hwmon3/pwm1 the fan can be controlled.