For 1990-2009 cars

### Single Fan

The engine cooling fan system consists of an electric cooling fan, two fan relays and a fan resistor.

The engine control module (ECM) controls cooling fan operation in either high speed or low speed mode, depending on cooling requirements. To activate the fan, the ECM applies ground to the coil side of the applicable fan relay. This energizes the coil and pulls the switch side of the relay closed.

In low speed operation, the ECM applies ground to the coil side of the low speed FAN LOW relay. This energizes the coil and applies voltage directly to the engine cooling fan resistor through the switch side of the FAN LOW relay. The cooling fan resistor is connected in series to the engine cooling fan. The series circuit operates the fan at low speed.

In high speed operation, the ECM applies a ground to the coil side of the high speed FAN HI relay. When energized, the FAN HI relay supplies voltage directly to the cooling fan through the switch side of the relay. With a direct voltage supply and path to ground the fan operates at high speed.

The cooling fan will always operate anytime the A/C system is operating. First at low speed, and then at high speed when engine coolant temperature exceeds a specified value.

### Dual Fans

The engine cooling fan system consists of 2 electrical cooling fans and 3 fan relays. The relays are arranged in a series parallel (S/P) configuration that allows the engine control module (ECM) to operate both fans together at low or high speeds, depending on cooling requirements. The cooling fans and fan relays receive battery positive voltage from the underhood fuse block.

In low speed operation, the ECM applies ground to the coil side of the low speed FAN LOW relay. This energizes the coil and applies voltage directly to the auxiliary cooling fan through the switch side of the FAN LOW relay. The fan is connected in series to the main cooling fan through the de-energized S/P FAN CNTRL relay. The series circuit operates both fans at low speed.

In high speed operation, the ECM applies a ground to the coil side of the FAN LOW relay, the S/P FAN CNTRL relay, and the high speed FAN HI relay. When energized, the FAN HI relay applies voltage directly to the main cooling fan through the switch side of the relay. Simultaneously, the FAN LOW relay and the S/P FAN CNTRL 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.

The cooling fans will always operate anytime the A/C system is operating. First at low speed, and then at high speed when engine coolant temperature exceeds a specified value.