4-Wire Pulse Width Modulation (PWM) Controlled Fans
Motherboard CPU Fan 4 Pin header Connector.
| Pin | Name | Color |
|---|---|---|
| 1 | GND | black |
| 2 | +12VDC | yellow |
| 3 | Sense | green |
| 4 | Control | blue |
For some AMD cpu fans:
| Pin | Name | Color |
|---|---|---|
| 1 | GND | black |
| 2 | +12VDC | red |
| 3 | Sense | yellow |
| 4 | Control | blue |
The 4-pin PWM fan connector was standardised by Intel’s 4-Wire Pulse Width Modulation (PWM) Controlled Fans Specification (Revision 1.2, July 2004; Revision 1.3, September 2005). It introduced closed-loop speed control for CPU cooling fans on ATX motherboards, replacing the earlier voltage-modulated 3-pin arrangement. The connector uses a 2.54 mm pitch keyed housing to ensure correct polarity, and the PWM control signal operates at a nominal frequency of 25 kHz. The standard is backwards compatible with 3-pin headers, allowing either connector type to be used on either header type, though with differing control capability.
Signals
- GND — Ground reference (black wire); return path for both power and signal circuits.
- +12VDC — 12 V supply at 12 V ±5 %; powers the fan motor directly.
- Sense — Tachometer output from the fan (open-collector, active-low); the fan generates 2 pulses per revolution, and the motherboard must supply a pull-up resistor to read the signal.
- Control — PWM speed-control input to the fan (open-collector/open-drain); the motherboard drives this signal at 25 kHz ±10 % (range 21–28 kHz) to vary fan speed. A high duty cycle increases speed; minimum fan RPM must not exceed 30 % of maximum rated RPM.
Notes
- Wire colours follow the Intel specification (black/yellow/green/blue for Intel-compatible fans). Some AMD-branded fans use red for the +12 V wire and yellow for the tachometer; the pinout and electrical behaviour are otherwise identical.
- Chassis and CPU fans may use either 3-pin or 4-pin power connectors. 3-pin connectors are usually used for the smaller chassis fans with lower power consumption. 4-pin connectors are usually used by CPU fans with higher power consumption. Fans and on-board fan headers are backwards compatible. Proper fan connector placement is shown in the figures below:
- Fan has a 3-pin power connector; desktop board has a 4-pin fan header:
Note: when using a 3-pin power connector with a 4-pin fan header, the fan will always be on; there is no fan control.
- Fan has a 4-pin power connector; desktop board has a 3-pin fan header:
- Fan has a 3-pin power connector; desktop board has a 4-pin fan header:
- The PWM control and tachometer lines are both open-collector; the motherboard supplies the necessary pull-up voltages.
- Fan operating voltage is 12 V ±5 %; the connector housing keying prevents reverse insertion.