For 1990-2009 cars

### Gasoline Engine

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 relay. This energizes the coil and applies voltage directly to the auxiliary cooling fan through the switch side of the low relay. The auxiliary fan is connected in series to the main cooling fan through the de-energized series/parallel (S/P) fan control 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 low speed fan relay, the fan control relay, and the high speed fan relay. When energized, the high speed fan relay applies voltage directly to the main cooling fan through the switch side of the relay. Simultaneously, the low speed fan relay and the S/P fan control 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 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.

### Diesel Engine

The engine cooling fan system consists of 2 electrical cooling fans, a cooling fan resistor, and 3 fan relays. The relays and cooling fan resistor are arranged in a 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 relay. This energizes the coil and applies voltage to the main cooling fan through the switch side of the low relay. The main cooling fan is connected in series to the low speed fan relay through the cooling fan resistor. The series circuit operates the main cooling fan at low speed.

In high speed operation, the ECM applies a ground to the coil side of the low speed fan relay, the fan control relay, and the high speed fan relay. When energized, the high speed fan relay applies voltage directly to the main cooling fan through the switch side of the relay. Simultaneously, the low speed fan relay and the fan control relay provide ignition voltage to the auxiliary cooling fan. With both fans connected directly to ground, 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.