Circuit/System Description
The fan 1 relay provides power to the fan control module. The fan control module completes the fan motor circuit by providing a path to ground. The module energizes the fan and controls fan speed according to instructions received from the powertrain control module (PCM).
The powertrain control module (PCM) controls cooling fan operation in either high speed or low speed mode, depending on cooling requirements. To activate a fan, the PCM applies ground to the coil side of the applicable fan relays. This energizes the coil and applies voltage directly to the cooling fan through the switch side of the relay.
The fan 1 relay provides power to the fan control module. The fan control module completes the fan motor circuit by providing a path to ground. The module energizes the fan and controls fan speed according to instructions received from the powertrain control module (PCM).
The powertrain control module (PCM) commands the fans ON in either high speed or low speed, depending on cooling requirements. In low speed, both fans are turned ON at a reduced speed. High speed has both fans turned ON at full speed.
In low speed operation, the PCM applies ground to the coil side of the low speed fan 3 relay. This energizes the coil and applies voltage directly to the auxiliary cooling fan through the switch side of the fan 3 relay. The fan is connected in series to the main cooling fan through the de-energized series/parallel (S/P) fan control 2 relay. The series circuit operates both fans at low speed.
In high speed operation, the PCM applies a ground to the coil side of the low speed fan 3 relay, the S/P fan 2 relay, and the high speed fan 1 relay. When energized, the high speed fan 1 relay applies voltage directly to the main cooling fan through the switch side of the relay. Simultaneously, the low speed fan 3 relay and the S/P fan 2 relay provide ignition voltage and a direct path to ground for the auxiliary cooling fan. With both fans connected in a parallel circuit, each fan receives full voltage and operates at high speed.