BRIDGE AS 4788539 - Caterpillar

Illustration 1 g01283808
Schematic of the Armbar/Seat Switches CircuitThis diagnostic code is associated with the Armbar/Seat Switches. These switches are connected to two inputs of the the ECM. One contact is normally open. The other contact is normally closed. Wire G984-PK is closed and wire G985-PU is open, when the Armbar is in the UP position. Wire G984-PK is open and wire G985-PU is closed, when the Armbar is in the DOWN position AND the Seat is OCCUPIED. If the Armbar is in the DOWN position and the Seat is UNOCCUPIED, BOTH circuits will be open. Refer to Table 1.
Table 1
Status of the Armbar/Seat Switch Circuit    
Armbar Position     Seat Status     G984-PK Circuit
J1-33     G985-PU Circuit
J2-58
   
Up     N/A     Closed     Open    
Down     Unoccupied     Open     Open    
Down     Occupied     Open     Closed    An FMI 04 diagnostic code is recorded when the status of both the inputs are grounded.The possible causes of this diagnostic code are listed below:
The "NORMALLY CLOSED" signal circuit (wire G984-PK) is shorted to ground.
The "NORMALLY OPEN" signal circuit (wire G985-PU) is shorted to ground.
The Armbar Switch has failed.
The Seat Switch has failed.
The ECM has failed. This is unlikely.System Response:The machine will be brought to a controlled stop. The park brake will be engaged. The implements will be locked out.Test Step 1. CHECK THE SWITCHES
Disconnect the negative battery cable and turn the key start switch to the OFF position.
Disconnect the Armbar switch and the Seat switch from the machine harness.
Connect one lead from a multimeter to contact A (wire 203-BK) of the connector for the Armbar switch.
Connect the other lead from a multimeter to contact B (wire G983-GN) of the connector for the Armbar switch.
Put the Armbar in the UP position.
Measure the resistance between contact A (wire 203-BK) and contact B (wire G983-GN). Note the resistance.
Put the Armbar in the DOWN position.
Measure the resistance between contact A (wire 203-BK) and contact B (wire G983-GN). Note the resistance.
Disconnect the lead from contact B (wire G983-GN) and connect the lead to contact C (wire G984-PK). Note the resistance.
Measure the resistance between contact A (wire 203-BK) and contact C (wire G984-PK). Note the resistance.
Put the Armbar in the UP position.
Measure the resistance between contact A (wire 203-BK) and contact C (wire G984-PK). Note the resistance.
Connect one lead from a multimeter to contact 1 (wire G983-GN) of the connector for the Seat switch.
Connect the other lead from a multimeter to contact 2 (wire G985-PU) of the connector for the Seat switch.
The Seat is UNOCCUPIED.
Measure the resistance between contact 1 (wire G983-GN) and contact 2 (wire G985-PU). Note the resistance.
Occupy the Seat.
Measure the resistance between contact 1 (wire G983-GN) and contact 2 (wire G985-PU). Note the resistance.Expected Result:The resistances agree with Table 1.The resistance from Armbar Switch contact A to contact B is greater than 5000 ohms when the Armbar is UP, and the resistance from contact A to contact B is less than 5 ohms when the Armbar is