How to control fan speed

This page discusses methods for controlling the system fan.

For Linux

Patched kernel

The Patch for controlling fan speed provides a convenient interface via /proc/acpi/ibm/fan.

Stock kernel, using ibm-acpi

If you have the ibm-acpi module loaded with experimental=1, you can control the fan without patching the kernel by directly writing to the relevant embedded controller register using /proc/acpi/ibm/ecdump.

For example:

# echo 0x2F 0x00 > /proc/acpi/ibm/ecdump (fan off)

# echo 0x2F 0x02 > /proc/acpi/ibm/ecdump (low speed)

# echo 0x2F 0x04 > /proc/acpi/ibm/ecdump (medium speed)

# echo 0x2F 0x07 > /proc/acpi/ibm/ecdump (maximum speed)

# echo 0x2F 0x80 > /proc/acpi/ibm/ecdump (automatic - default)

# echo 0x2F 0x40 > /proc/acpi/ibm/ecdump (disengaged)

Ssee the specifications below for the meaning of these modes.

Automated control scripts

See ACPI fan control scripts.

For Windows

Shimodax's ThinkPad fan control tool (see the forum discussion at thinkpads.com).

Hardware specs

The patch relies on the following hardware behavior, which was discovered experimentally by Thinker and neither provided by nor confirmed by IBM/Lenovo. The following description may be inaccurate and may vary by model (see list of models above). The terminology probably does not match the one used by IBM/Lenovo engineers.

ACPI DSDT register _SB.PCI0.LPC.EC.HFSP (8 bits, offset 0x2F in the EmbeddedController address space, accessed through the standard EC interface at IO ports 0x62 and 0x66) is read/writable and has the following meaning:

Bits   7 6 5 4 3 2 1 0
       ---------------
Value  1 0 * * * * * *  - automatic
       * 1 * * * * * *  - disengaged
       0 0 N N N N N N  - manual (0..63; 0=disable fan, 1=min, ..., 7=max)

In automatic mode, the embedded controller sets the fan speed automatically according to system temperatures and some unknown algorithm.

In manual mode, the fan level is forced to the given value and the EC will auto-regulate the fan to maintain at a (roughly) constant RPM, which is model-dependent. Manual speed levels 8-63 yield the same behavior as level 7, and the the ACPI DSDT uses level 7 for the emergency mode it enters upon critical CPU/GPU temperature, so apparently 7 is the real maximum level.

In disengaged mode, the embedded controller does not read the fan RPM (hence EmbeddedController offset 0x84 is not updated), and does not maintain a stable fan speed. When disengaged mode is entered the fan speed is not immediately changed (except if the fan was disabed, in which case it is turned on at a low level). However, once in disengaged mode, fan speed will slowly increase to beyond the maximum manual level (this may cause hardware damage!).

After boot, the register may not reflect the true state of the EC (on some models it reads 0x07 even though the EC is actually in automatic mode).

Hint:

Apparently the pulsing fan noise experienced by some users can be cured by repeatedly running 2-4 seconds of manual control followed by 0.5-1 seconds of disengaged mode. The pulse occurs when the the embedded controller computes the fan speed and adjusts the fan voltage adaptively every few seconds (~4.8sec for the ThinkPad T43); the aforementioned mode switching doesn't give it a chance to do so. One of the ACPI fan control scripts implements this solution.

Supported models

The above was successfully tested on the following models:

• ThinkPad T43, T43p (fan levels RPM: 1-2 = ~3300, 3-5 = ~4100, 6-7 = ~4700; disengaged mode works)
• ThinkPad T42, T42p (fan levels RPM: 1-2 = ~2900, 3-5 = ~3700, 6-7 = ~4700)
• ThinkPad T41, T41p (fan levels RPM: 1-2 = ~2980, 3-5 = ~3500, 6-7 = ~4050; disengaged mode works at ~5100)
• ThinkPad T40 (fan levels RPM: 1-2 = ~2950, 3-5 = ~3600, 6-7 = ~4050)
• ThinkPad T22
• ThinkPad T23
• ThinkPad R52
• ThinkPad R50 (highest manual level is 3; disengage mode works and reaches much higher RPM)
• ThinkPad X41 Tablet
• ThinkPad X31
• ThinkPad Z60t (fan levels RPM: 1-2 = ~1700, 3-5 = ~2800, 6-7 = ~3500)

Probably other models are supported too (please update this page if you confirm this).

The following models also work, use a different access method which supported (only) via the /proc/acpi/ibm/fan of ibm-acpi even on stock kernels (no need for patching).

• ThinkPad 600E, 600X, 770E, 770X (these use a different fan control interface)

Unsupported models

• ThinkPad 560 (these models don't have a fan)