FAN GP-BLOWER 2173572 - Caterpillar

Illustration 1 g00805012
Schematic for the Fine Modulation SwitchThis switch has two inputs to the ECM. The inputs are normally open and normally closed. During proper operation, one input is open and the other input is grounded. This diagnostic code is recorded when the status of both the normally open inputs and the normally closed inputs are open.
Table 1
Status of the Fine Modulation Switch    
Switch Position     J1-36 (wire T870-18-BR) N/O (1)     J1-37 (wire T869-18-WH) N/C (2)    
Normal     Ground     Open    
Activated     Open     Ground    
( 1 ) N/O means Normally Open
( 2 ) N/C means normally closed or groundedSystem Response:The machine response is listed:
The fine modulation mode cannot be activated.
The fine modulation mode is deactivated if the service code is currently active.Note: The following procedure can create other related diagnostic codes. Complete the following procedure. Then clear the related diagnostic codes.Note: Ensure that the diagnostic code is active.Test Step 1. CHECK THE SWITCH.
Turn the disconnect switch and the key start switch to the OFF position.
Disconnect the J1 harness connector from the ECM.
Place the switch in the OFF position (N/C).
At the switch, measure the resistance between contact 2 (wire 953-18-GY) and contact 1 (wire T870-18-BR). Note the resistance.
Hold the switch in the ON position (N/O).
At the switch, measure the resistance between contact 2 (wire 953-18-GY) and contact 3 (wire T869-18-WH). Note the resistance.Expected Result:The resistance should be less than 5000 ohms for each measurement.Results:
YES - The resistance is less than 5000 ohms. The switch is correct. Proceed to Test Step 2.
NO - The resistance is greater than 5000 ohms. The switch has failed.Repair: Replace the switch. Verify that the new switch corrects the problem. Stop.Test Step 2. CHECK THE RETURN CIRCUIT.
The key start switch and the disconnect switch remain in the OFF position.
The J1 harness connector remains disconnected from the ECM.
Measure the resistance from contact 2 (wire 953-18-GY) of the switch to contact J1-15 (wire 953-18-GY).Expected Result:The resistance should be less than 5000 ohms.Results:
YES - The resistance is less than 5000 ohms. The return circuit is correct. Proceed to Test Step 3.
NO - The resistance is greater than 5000 ohms. There is an open in the return circuit.Repair: Repair the harness or replace the harness. Stop.Test Step 3. CHECK THE RESISTANCE OF THE N/C CIRCUIT.
The key start switch and the disconnect switch remain in the OFF position.
The