CYL GP- 4941828 - 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 normally closed inputs are grounded.
Table 1
Status for 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 groundedThe possible causes of this diagnostic code are listed:
The normally open circuit is shorted to ground while the normally closed circuit is grounded through the switch.
The normally closed circuit is shorted to ground while the normally open circuit is grounded through the switch.
The normally open circuits and the normally closed circuits are shorted to ground in the harness.
The normally open circuits and normally closed circuits are shorted together. The switch must be in one specific position.
The switch has failed.System Response:The machine response is listed:
The fine modulation mode cannot be activated.
Thefine modulation mode is deactivated if the diagnostic code is active.Note: The following test procedure may create other diagnostic codes. Ignore these created diagnostic codes and clear the diagnostic codes when the original diagnostic code is corrected.Note: Ensure that the diagnostic code is active.Test Step 1. CHECK THE SWITCH.
Observe ON/OFF status of the diagnostic code.
Disconnect the connector of the switch from the harness.Expected Result:The diagnostic code remains active.Results:
YES - The diagnostic code remains active. The switch is not the cause of the diagnostic code. Proceed to Test Step 2.
NO - The diagnostic code is inactive. The switch has failed or the harness has failed.Repair: Repeat this test in order to verify the failure of the switch. Repair the switch or replace the switch. Repair the harness or replace the harness. Stop.Test Step 2. CHECK THE RESISTANCE OF THE N/C WIRE.
Turn the key start switch and the disconnect switch to the OFF position.
The return wire remains disconnected from the switch.
Disconnect the J1 and J2 harness connector from the ECM.
Measure the resistance between contact J1-36 (wire T870-18-BR) and all sources of ground.Expected Result:The resistance should be greater than 5000 ohms.Results:
YES - The resistance is greater than 5000 ohms. The N/C circuit of the harness is correct. Proceed to Test Step 3.
NO - The resistance is less than 5000 ohms.Repair: The harness has failed. There is a short in the harness. The short is in the N/C wire (T870-BR) and the circuit with the low resistance. Repair the harness or replace the harness. Verify that the repair corrects the problem. Stop.Test Step 3. CHECK THE RESISTANCE OF THE N/O WIRE.
The conditions of the previous test remain intact.
Measure the resistance between contact J1-37 (wire T869-18-WH) and all sources of ground.Expected Result:The resistance is greater than 5000 ohms.Results:
YES - The resistance is greater than 5000 ohms.Repair: It is unlikely that the