HARNESS AS 3529456 - Caterpillar

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 motor by allowing oil to bypass the fan motor. The fan pump drives the fan. When the ECM outputs minimum current to the engine fan control solenoid, less oil is bypassed. The fan motor 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 motor 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 in the electronic service tool. The override allows the fan to be manually changed from the minimum to the maximum rpm.The cooling fan bypass solenoid prevents operation of the fan when the engine is cold. When the engine has warmed up, the solenoid will open the valve to allow hydraulic pressure to flow to the fan motor.During the following procedure, refer to the electrical schematic for the application.Complete the procedure in the order in which the steps are listed.
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 connectors are free of debris and connected securely.
C. Connect the electronic service tool to the diagnostic connector.
D. Restore the electrical power to the ECM.
E. Select diagnostic tests on the electronic service tool.
F. Select the "Override Parameters" screen.
G. Activate the fan override.
H. Monitor the active diagnostic code screen on the electronic service tool. Check and record any active diagnostic codes. Wait at least 30 seconds in order for the diagnostic code to become active.
I. Disable the fan override.
Active Diagnostic Codes
Result: No diagnostic codes are active.
The problem may have been related to a faulty connection in the harness. Carefully inspect the connectors and wiring. Refer to Troubleshooting, "Electrical Connectors - Inspect".
Result: A 4212-6 or 291-6 code is active at this time.
Proceed to Test Step 2.
Result: A 4212-5 or 291-5 code is active at this time.
Proceed to Test Step 3.
Result: A 1076-6 code is active at this time.
Proceed to Test Step 4.
Result: A 1076-5 code is active at this time.
Proceed to Test Step 5.
2. Disconnect the Connector for the Engine Fan Control Solenoid in Order to Create an Open Circuit
A. Remove the electrical power from the ECM.
B. Disconnect the connector for the engine fan control solenoid.
C. Restore the electrical power to the ECM.
D. Activate the fan override.
E. Monitor the active diagnostic code screen on the electronic service tool. Check and record any active diagnostic codes. Wait at least 30 seconds in order for the diagnostic code to become active.
F. Disable