WASHER-THRUST 8D7425 - Caterpillar

System Operation Description:Use this procedure to troubleshoot the electrical system if a problem is suspected with the engine fan control solenoid. Use this procedure if one of the diagnostic codes in Table 1 is active.
Table 1
Diagnostic Codes Table    
CDL Code     J1939 Code     Code Description
(code descriptions may vary)     Comments    
291-5     4212-5     Engine Cooling Fan Solenoid : Current Below Normal     The Electronic Control Module (ECM) detects an open circuit in the circuit for the engine fan control solenoid.
The ECM sends minimum current to the fan control solenoid. The code is logged.    
291-6     4212-6     Engine Cooling Fan Solenoid : Current Above Normal     The ECM detects a short circuit to ground in the circuit for the engine fan control solenoid.
The ECM sends minimum current to the fan control solenoid. The code is logged.    
1076-5         Engine Cooling Fan Bypass Solenoid : Current Below Normal     The Electronic Control Module (ECM) detects an open circuit in the circuit for the engine cooling fan bypass solenoid.
The ECM sends minimum current to the fan control solenoid. The code is logged.    
1076-6         Engine Cooling Fan Bypass Solenoid : Current Above Normal     The ECM detects a short circuit to ground in the circuit for the engine cooling fan bypass solenoid.
The ECM sends minimum current to the fan bypass solenoid. The code is logged.    The ECM monitors engine coolant temperature, intake manifold air temperature, and hydraulic oil temperature. The ECM monitors the sensors in order to determine the correct speed for the engine cooling fan.The ECM controls the speed of the fan by controlling the current to the engine fan control solenoid. The engine fan control solenoid controls the amount of pressure to the fan pump by allowing oil to bypass the fan pump. The fan pump drives the fan. When the ECM outputs minimum current to the engine fan control solenoid, less oil is bypassed. The fan pump will now drive the fan at a higher rpm. When the ECM outputs maximum current to the engine fan control solenoid, more oil is bypassed. The fan pump will now drive the fan at a lower rpm.If the ECM detects a system fault, the ECM provides minimum current to the solenoid. Minimum current ensures a maximum fan speed while the fault condition exists.An override is available with Caterpillar Electronic Technician (ET). An override allows the fan to be manually changed from the minimum to the maximum rpm.
Illustration 1 g02061556
Schematic for the engine fan control solenoid
Table 2
Troubleshooting Test Steps    Values    Results    
1. Check for Active Diagnostic Codes
A. Remove the electrical power from the ECM.
B. Verify that the solenoid connector is free of debris and connected securely.
C. Connect Cat ET to the service tool connector.
D. Restore the electrical power to the ECM.
E. Select diagnostic tests from Cat ET.
F. Select the "Override Parameters" screen