Circuit/System Description

The radiator cooling fan is controlled with a pulse width modulated (PWM) signal on the cooling fan relay control circuit from the hybrid/EV powertrain control module 2. Although the hybrid/EV powertrain control module 2 is directly connected to the cooling fan, the ECM is considered the master controller. The ECM sends a fan command PWM signal to the hybrid/EV powertrain control module 2 through the cooling fan signal hardwire circuit. The hybrid/EV powertrain control module 2 operates in a pass-through mode for any ECM-derived fan request. The higher the duty cycle the higher the cooling fan speed.

When the ECM is awake and there are no faults, the hybrid/EV powertrain control module 2 sends its cooling fan requests to the ECM via serial data. The ECM uses this request and other vehicle inputs to decide if and what speed the cooling fan should operate. The ECM sends a processed cooling fan signal command back to the hybrid/EV powertrain control module 2 via a PWM signal. The hybrid/EV powertrain control module 2 sends the fan relay control PWM signal to the cooling fan to operate and at what speed.

If the vehicle is in Charge Mode and the hybrid/EV powertrain control module 2 requests the cooling fan to operate and the ECM is not awake, the hybrid/EV powertrain control module 2 will directly control the cooling fan. If active cooling is needed, the ECM wakes up to operate the air conditioning control module and then the ECM is the master controller for the fan.