Customize Xiaomi AX9000 Fan Control With Automatic Temperature-Based Speed Adjustment

Introduction

The Xiaomi AX9000 has a cooling fan, but on my stock firmware its default activation threshold is 104°C. With a threshold that high, the fan barely gets a chance to run. To make it respond to your own temperature settings, you can take over fan control, read the temperatures, and write directly to the PWM node.

I have tested the control strategy and hardware interfaces described here on my own AX9000. This article explains how the adjustment works and provides a standalone installation script for changing thresholds, checking the running state, and restoring stock fan control.

Prerequisites

First, enable SSH access to the router. I use xmir-patcher. Follow the project instructions to enable SSH, then connect as root:

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ssh root@192.168.31.1

Replace the IP address with your router’s address. Except for uploading the script, run all subsequent commands in the router’s SSH session.

This guide targets the AX9000’s stock firmware and uses its built-in thermaltool and procd. First, check that the fan nodes exist:

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ls /sys/devices/platform/soc/78ba000.i2c/i2c-1/1-002f/

We need pwm1 and fan1_input in that directory. Before installing, the script checks these nodes, all six temperature readings, and the service management interface. Other firmware may use different paths or temperature tools, so these commands cannot be applied directly to every installation.

If you already have another fan control script installed, disable it and restore the stock services it changed before installing this one. This avoids two programs adjusting the fan at the same time. The installer checks mobile_accel for common signs of a custom temperature controller; it does not reconstruct files modified by another script.

How the Adjustment Works

Reading Six Temperatures

This strategy reads three thermal zones and three wireless interfaces. Their order in the configuration file matches the table below.

The first three paths are under /sys/devices/virtual/thermal/. For example, you can inspect a thermal zone and a wireless temperature with:

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cat /sys/devices/virtual/thermal/thermal_zone4/temp
thermaltool -i wifi0 -get

The script converts readings to whole degrees Celsius. If a node returns millidegrees, such as 45000, it divides the value by 1000 to obtain 45. For wireless temperatures, it uses the output format of the firmware covered here: the third field of the line containing temp, with commas removed.

These readings are identified by their interface numbers. The exact hardware represented by thermal_zone4 through thermal_zone6 depends on the firmware, so those names should not be assumed to identify particular chips.

Calculating the Fan Level

The logical fan level ranges from 0 to 134. Level 0 stops the fan, while 134 is the highest level used by this strategy. These levels are neither RPM values nor the hardware maximum of the PWM interface.

First, add up the six current temperatures, high thresholds, and low references:

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T = sum of the six current temperatures
H = sum of the six high thresholds
L = sum of the six low references - 6

Slope = 134 / (H - L), rounded to three decimal places
Target level = integer part of Slope × (T - L)

The result is limited to the range 0 to 134. With the default configuration, H = 341, L = 251, and the slope is approximately 1.489. For temperatures of 45, 46, 46, 54, 54, 55, the sum is 300, giving a target level of 72.

There is also a check for each individual reading: if any temperature reaches its own high threshold, the target level becomes 134. This prevents cooler readings elsewhere from masking a hot sensor in the total.

The low references define the starting point of the speed curve. They are not separate temperatures at which each sensor stops the fan, and this algorithm is not a hysteresis switch that turns on at one threshold and off at another. For example, if all six readings equal their default low references, their sum is 257, and the target level is still approximately 8.

Writing PWM and Adjusting Speed Gradually

The logical level is converted before it is written to pwm1:

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Level = 0: write PWM 0
Level > 0: write PWM (Level + 30)

For example, level 72 corresponds to PWM 102, and level 134 corresponds to PWM 164. Actual fan speed is read from fan1_input; the PWM value and RPM are different measurements.

The control loop runs once per second. In automatic mode, the current level moves one step toward the target on each iteration. This reduces abrupt speed changes caused by fluctuating temperatures. The same rule applies when a sensor reaches its high threshold: the target changes immediately, while the current level increases gradually. Going from level 0 to 134 takes approximately 134 seconds.

If the script cannot read all six temperatures, it writes PWM 164 immediately and records sensor-error in the log. This error handling bypasses the gradual increase.

Taking Over Stock Fan Control

If both the custom program and the stock controller write to pwm1, they will overwrite each other’s settings. Installation therefore removes root cron entries containing mitempcontrol and handles the echo lines in statisticsservice related to temperature control registration or PWM writes.

The script removes only lines in statisticsservice that contain both echo and either tempcontrol or pwm1, preserving other output. Whenever the new service starts, it also terminates existing stock tempcontrol processes found in the process list. This targets the stock service layout covered here. If your firmware restarts its controller through another service, identify that startup entry first.

The new program is installed as /usr/sbin/ax9000-fan, with its service script at /etc/init.d/ax9000-fan. It uses procd’s command and respawn interfaces to manage the process. Once enabled, the service starts the control loop when the router boots.

One-Command Installation

Download the complete script below. It runs with the router’s /bin/sh and does not require Bash or Python.

Run this command in the router’s SSH session:

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curl -fL https://www.jamesflare.com/ax9000-fan-control/ax9000-fan.sh -o /tmp/ax9000-fan.sh && sh /tmp/ax9000-fan.sh install

If the router does not have curl, download the script on your computer and upload it from there:

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scp -O ax9000-fan.sh root@192.168.31.1:/tmp/ax9000-fan.sh

The -O option uses the traditional SCP protocol, which works with routers that do not provide an SFTP service. After uploading, return to the router’s SSH session and run:

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sh /tmp/ax9000-fan.sh install

The installer saves the original statisticsservice and root crontab in /etc/ax9000-fan-backup/, creates the default configuration, and enables and starts the service. It preserves an existing nonempty /etc/temp.conf. Reinstalling also preserves the backup made during the first installation.

Changing the Configuration

The configuration is stored in /etc/temp.conf. Its default contents are:

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52 38
53 39
53 39
61 47
61 47
61 47
手动指定档位：0

Each of the first six lines contains the high threshold followed by the low reference for one reading, in the order shown in the temperature table. Both values are whole degrees Celsius, and the high threshold must be greater than the low reference. Missing values, nonnumeric values, or invalid threshold pairs fall back to that line’s defaults.

Edit the file with vi:

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vi /etc/temp.conf

Alternatively, write the whole file at once:

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cat > /etc/temp.conf <<'EOF'
52 38
53 39
53 39
61 47
61 47
61 47
手动指定档位：0
EOF

The script reads the configuration every second, so saved changes take effect on the next iteration without restarting the service. Lowering a high threshold makes that reading trigger the highest target level sooner. Changing the low references changes the overall speed curve. Start with the defaults, observe normal workloads, and adjust gradually.

On the seventh line, 0 selects automatic speed control. A positive integer selects a fixed level, for example:

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手动指定档位：60

This immediately sets level 60, corresponding to PWM 90. Values above 134 are limited to 134. The Chinese label means “manually specified level”; keep the line as shown, including the full-width colon ：, to use the same configuration format as the Chinese version.

Checking the Running State

View the latest iteration’s status:

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cat /tmp/fan.log

Here is an example after automatic control has reached its target:

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[ 2026-09-29 18:10:00 ]
mode=auto level=72 target=72 hot=0 rpm=1800
highest_level=72 highest_rpm=1800
temperatures: 45 46 46 54 54 55
thresholds (high low x6, manual): 52 38 53 39 53 39 61 47 61 47 61 47 0

level is the current level, target is the level calculated from the temperatures, hot=1 means at least one reading has reached its high threshold, and rpm is the measured fan speed. The example RPM illustrates the log format; it does not mean level 72 always produces that speed.

highest_level and highest_rpm record the highest values since the service started. Restarting the service resets them. The log is overwritten every second in /tmp, rather than continuously appended to flash storage.

You can also read the actual PWM and fan speed directly:

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cat /sys/devices/platform/soc/78ba000.i2c/i2c-1/1-002f/pwm1
cat /sys/devices/platform/soc/78ba000.i2c/i2c-1/1-002f/fan1_input

If the log stops updating, inspect the service and error output:

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ubus call service list '{"name":"ax9000-fan"}'
logread | tail -n 50

Use these commands to manage the service:

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/etc/init.d/ax9000-fan restart
/etc/init.d/ax9000-fan stop
/etc/init.d/ax9000-fan start

Stopping the service sets PWM to 164 to maintain airflow. Stopping the custom service alone does not restart stock fan control.

Restoring Stock Fan Control

Run these commands on the router:

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sh /usr/sbin/ax9000-fan uninstall
reboot

Uninstalling stops the custom service, disables its automatic startup, and restores the first backup of statisticsservice. For root’s crontab, it restores only the backed-up entries containing mitempcontrol, preserving other current jobs. After rebooting, stock fan control runs through its original startup sequence.

The backup, configuration, and disabled custom service files are retained for inspection. If you modified statisticsservice after installation, merge those changes yourself before restoring it, because restoration replaces the entire file with the backup. The backup represents the state before the first installation of this script.

Firmware upgrades may overwrite service files or change hardware nodes. After upgrading, check the temperature and fan interfaces again, and do not restore an old firmware’s backup directly onto a new firmware version.