ENGINE AR-COMPLETE 4324767 - Caterpillar

Electronic Control Module (ECM) controls the rpm of the engine fan in order to provide the following benefits:
Reduced noise from the fan
Improved fuel economy
Reduced overcoolingThe engine's ECM controls the rpm of the engine fan by varying the current to the engine fan control solenoid. The engine fan control solenoid controls hydraulic oil pressure to the fan pump. The fan pump supplies hydraulic oil to the hydraulic fan motor.The engine cooling fan pump pressure sensor provides feedback to the ECM about the hydraulic oil pressure that is available at the fan pump. The ECM compares the fan pump pressure to a set of maps stored in the software of the ECM. The maps are based on the engine coolant temperature and on the engine rpm. By using the engine coolant temperature and the pump pressure, the ECM calculates the desired fan drive pump pressure. If the fan's actual pump pressure is different from the calculated pressure, the ECM will vary the current to the engine fan control solenoid in order to change the pump pressure to the desired pressure.Note: The software in the ECM can use the coolant temperature, the inlet manifold temperature, and the aftercooler temperature in the calculations for the pump pressure. Machines with the serial number prefix of 9TR and 9XR, the ECM uses the coolant temperature sensor. Machines with the serial number prefix of 7PZ and AAF, the ECM uses the coolant temperature sensor and either an aftercooler temperature sensor or an inlet manifold temperature sensor. The software uses the highest temperature between the coolant temperature and the aftercooler temperature or the inlet manifold temperature in the calculations.When the engine coolant temperature is low, the ECM limits fan rpm to a low rpm. As the engine coolant temperature rises, the ECM increases fan rpm. If engine coolant temperature continues to rise the ECM increases fan rpm until the engine coolant temperature stabilizes.Note: Machines with the serial number prefix of 7PZ and AAF have a restriction on fan rpm that is based on the altitude.The current to the engine fan control solenoid is a pulse width modulated signal. The signal varies between 0.4 amperes (maximum fan rpm) to 1.8 amperes (minimum fan rpm). The ECM adjusts the current to the engine fan control solenoid in order to keep the fan rpm within 50 rpm of the desired rpm.An override is available with the Caterpillar Electronic Technician (ET). This allows the fan to be manually changed from the minimum to the maximum possible rpm. If the ECM detects a problem with the solenoid circuit, a diagnostic code is generated. The current to the solenoid is set to the minimum value.