EDGE-END 5239783 - Caterpillar

Illustration 1 g00606592
Schematic Of The Rear Steer Toggle Switch
Table 1
ECM Contact     Switch Contact     Wire Number     Left     Hold     Right    
24     Left Steer     B843-BR     Gnd     Opn     Opn    
21     Right Steer     B844-OR     Opn     Opn     Gnd    
39     Ground Return     840-GN     Gnd     Gnd     Gnd    The Rear Steer Manual Switch has two inputs to the ECM. During normal operation, neither switch input is returned (grounded) except when the switch is depressed. The preceding chart shows the continuity of each switch circuit for the three positions of the switch. When a circuit is measured with a voltmeter, an open circuit will measure 5 DCV and a returned circuit will measure approximately 0 DCV. A failure is detected when the status of both inputs is returned (grounded). A CID 040 FMI F12 diagnostic code (fault) is recorded when the status of both inputs is returned (grounded). he results of this diagnostic code are:
A category 2 warning is showing on the Computerized Monitoring System.
The manual steering will not work until this diagnostic code is no longer present. The possible causes of this diagnostic code are:
Return circuit (840-GN) is open.
Signal circuit 1 (B843-BR) is grounded.
Signal circuit 2 (B844-OR) is grounded.
Switch is faulty.
ECM is faulty (unlikely). Service Note: Ensure that the CID 040 FMI F12 is on-hold and that the diagnostic code is present. If the diagnostic code (fault) present indicator is not ON toggle the switch until it is in the position where the diagnostic code present indicator is ON.
Check the Steer Left Circuit For Proper Operation. This step checks the continuity of the Steer Left circuit in the machine harness and the switch.
Turn the key start switch to the OFF position.
Disconnect the machine harness connector from the ECM.
Place the both rear steer switch in the center position.
At the machine harness connector for the ECM, check continuity from contact 24 (B843-BR) to contact 39 (840-GN). Expected Result: With the rear steer switch in the left position there should be CONTINUITY. With the switch in the center position, there should be NO CONTINUITY. Results:
YES - Proceed to Step 3.
NO - The switch or the machine harness is faulty. Proceed to the next step.
Check the Steer Left Circuit Of The Switch. This check determines whether the switch or the machine harness is faulty.
Disconnect wire B843-BR (terminal 1) and wire 840-GN (terminal 2) from the rear steer switch.
At the switch, check for continuity between terminal 1 and 2. Expected Result: With the rear steer switch in the left position there should be CONTINUITY. With the switch in the center position, there should be NO CONTINUITY. Results:
YES - The machine harness is faulty. Either the steer left circuit (B843-BR) or the return circuit (840-GN) is open in the machine harness. Repair or replace the machine harness. STOP.
NO - The switch is faulty. Replace the rear steer switch with the faulty readings. STOP
Check