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, the fans are configured in series. In high speed, the fans are configured in parallel.
In low speed operation, the ECM applies ground to the coil side of the fan 1 relay. Voltage is applied directly to the right cooling fan through the switch side of the fan 1 relay, which is fed by the fan 1 fuse. The left fan is connected in series to the left fan through the de-energized fan 2 relay so that both operate at low speed.
In high speed operation, the ECM applies a ground to the coil side of the fan 1 relay, the fan 2 relay and the fan 3 relay. Voltage is applied directly to the left cooling fan through the switch side of the relay, which is fed by the fan 2 fuse. The left cooling fan obtains voltage through the fan 1 relay and ground through the fan 2 relay.
The ECM monitors the low and high speed cooling fan relay control circuits for the following conditions
- Short to ground
- Short to voltage
- An open circuit
If the ECM detects an improper voltage level on the low or high speed ECM driver circuits, then DTC P0480 or P0481 will set and the affected ECM driver will be disabled.
Description and Operation
Cooling Fan Description and Operation
The engine control module (ECM) uses the engine coolant temperature (ECT) sensor to monitor the engine for an over-temperature 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 the cylinders, the ECM is able to reduce the temperature of the coolant.
- «Cooling System Description and Operation»(ref-275043-S36509922592007122600000)
- «Instrument Cluster Description and Operation»(ref-275011-S08294840582007122600000)
- «Indicator/Warning Message Description and Operation»(ref-275011-S03171139942007122600000)
- «Audible Warnings Description and Operation»(ref-275011-S16944281372007122600000)
The instrument panel cluster (IPC) illuminates the TEMP indicator when the engine control module (ECM) determines that the coolant temperature is more than 128°C (262°F). The IPC receives a discrete input from the ECM requesting illumination.
The IPC illuminates the TEMP indicator during the display test at the start of each ignition cycle.
- «INSTRUMENT CLUSTER DESCRIPTION AND OPERATION»(ref-275011-S08294840582007122600000)
- «Cooling Fan Description and Operation»(ref-275043-S09688275772007122600000)
- «Engine Overheating»(ref-275043-S24750515192007122600000)
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 fan 1 relay. This energizes the coil and applies voltage directly to the right cooling fan through the switch side of the fan 1 relay, which is fed by the fan 1 fuse. The left fan is connected in series to the right fan through the de-energized fan 2 relay so that both operate at low speed.
In high speed operation, the ECM applies a ground to the coil side of the fan 1 relay, the fan 2 relay and the fan 3 relay. On the fan 3 relay, the energized coil closes the switch side of the relay and applies voltage directly to the left cooling fan through the switch side of the relay, which is fed by the fan 2 fuse. At the same time, the ECM energizes fan 2 relay pulling the switch side over, providing a direct path to ground for the right cooling fan, which has voltage applied through the energized fan 1 relay. In high speed mode, the fans are operated as a parallel circuit with full voltage applied to each.
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 fan 1 relay. This energizes the coil and applies voltage directly to the right cooling fan through the switch side of the fan 1 relay, which is fed by the fan 1 fuse. The right fan is connected in series to the left fan through the de-energized fan 2 relay so that both operate at low speed.
In high speed operation, the ECM applies a ground to the coil side of the fan 1 relay, the fan 2 relay and the fan 3 relay. On the fan 3 relay, the energized coil closes the switch side of the relay and applies voltage directly to the left cooling fan through the switch side of the relay, which is fed by the fan 2 fuse. At the same time, the ECM energizes fan 2 relay pulling the switch side over, providing a direct path to ground for the right cooling fan, which has voltage applied through the energized fan 1 relay. In high speed mode, the fans are operated as a parallel circuit with full voltage applied to each.
Cooling Fan Description and Operation
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.