Circuit/System Description
The engine control module (ECM) 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 ECM applies ground to the coil side of the low speed fan 1 relay. This energizes the coil and applies voltage directly to the left cooling fan through the switch side of the low relay. The left fan is connected in series to the right cooling fan through the de-energized series/parallel (S/P) fan 2 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 1 relay, the S/P fan 2 relay, and the high speed fan 3 relay. When energized, the high speed fan 3 relay applies voltage directly to the right cooling fan through the switch side of the relay. Simultaneously, the low speed fan 1 relay and the S/P fan 2 relay provide ignition voltage and a direct path to ground for the left cooling fan. With both fans connected in a parallel circuit, each fan receives full voltage and operates at high speed.
The engine control module (ECM) uses the engine coolant temperature (ECT) sensor to monitor the engine for an over-termperature condition. This condition occurs when the coolant temperature is above a calibrated value for a calibrated length of time. The ECM will disable half of the cylinders by turning OFF the fuel injectors. By disabling half of cylinders, the ECM is able to reduce the temperature of the coolant.
The engine cooling fan system consists of 2 electrical cooling fans and 3 fan relays. The relays are arranged in a series/parallel configuration that allows the engine control module (ECM), or powertrain control module (PCM), to operate both fans together at low or high speeds. The cooling fans receive positive voltage from the cooling fan relays which receive battery positive voltage from the underhood fuse block.
During low speed operation, the ECM or PCM supplies the ground path for the low speed fan relay, which is fan 1 relay, through the low speed cooling fan relay control circuit. This energizes the low speed fan relay coil, closes the relay contacts, and supplies battery positive voltage from the fan 1 fuse through the cooling fan motor supply voltage circuit to the left cooling fan. The ground path for the left cooling fan is through the series/parallel relay, which is fan 2 relay, and the right cooling fan. The result is a series circuit with both fans running at low speed.
During high speed operation the ECM or PCM supplies the ground path for the low speed fan relay through the low speed cooling fan relay control circuit. The ECM or PCM grounds the high speed fan relay, which is fan 3 relay, and the series/parallel relay through the high speed cooling fan relay control circuit. This energizes the series/parallel relay coil, closes the relay contacts, and provides a ground path for the left cooling fan. At the same time the high speed fan relay coil is energized closing the relay contacts and provides battery positive voltage from the fan 2 fuse on the cooling fan motor supply voltage circuit to the right cooling fan. During high speed fan operation, both engine cooling fans have their own ground path. The result is a parallel circuit with both fans running at high speed.
The engine control module (ECM) 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 ECM applies ground to the coil side of the low speed fan 1 relay. This energizes the coil and applies voltage directly to the left cooling fan through the switch side of the low relay. The left fan is connected in series to the right cooling fan through the de-energized series/parallel (S/P) fan 2 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 1 relay, the S/P fan 2 relay, and the high speed fan 3 relay. When energized, the high speed fan 3 relay applies voltage directly to the right cooling fan through the switch side of the relay. Simultaneously, the low speed fan 1 relay and the S/P fan 2 relay provide ignition voltage and a direct path to ground for the left cooling fan. With both fans connected in a parallel circuit, each fan receives full voltage and operates at high speed.
The optional coolant heater operates using 110-volt AC external power and is designed to warm the coolant in the engine block area for improved starting in very cold weather. There is an internal thermal switch in the power cord that prevents operation above -18°C (0°F). The coolant heater helps reduce fuel consumption when a cold engine is warming up. The unit is equipped with a detachable AC power cord. A weather shield on the cord is provided to protect the plug when not in use.
Cooling System Description and Operation
The cooling systems function is to maintain an efficient engine operating temperature during all engine speeds and operating conditions. The cooling system is designed to remove approximately one-third of the heat produced by the burning of the air-fuel mixture. When the engine is cold, the coolant does not flow to the radiator until the thermostat opens. This allows the engine to warm quickly.