PWM Fan Control Module - 4.0L: Operation
WARNING: This page is about a different car, the 2004 Jeep Grand Cherokee. However, it is still accessible from the selected car via links, so may be relevant.
The PWM relay is used to control the speed of the electric radiator cooling fan. It allows for multiple fan speeds. This allows for improved fan noise and A/C performance, better engine cooling, and additional vehicle power.
PWM relay operation is controlled by the Powertrain Control Module (PCM). To operate the PWM relay, the PCM looks at inputs from:
- Engine coolant temperature
- Ambient temperature from the body controller
- Vehicle speed
- Transmission oil temperature
- A/C switch position (A/C request)