HUB R.H. 0004129 - Caterpillar

Illustration 1 g01389548
Compression Brake Switch connections
The compression brake switch is equipped on the 24M Motor Grader.The compression brake switch is a two-pole, double-throw switch. One pole is used to provide two switch to ground inputs to the ECM to indicate the status of the switch. The other switch pole is not used for ECM operation.During normal operation, one of the inputs is not connected to ground and the other input is connected to ground through the switch contacts. An internal pull-up voltage is present at the ECM switch inputs. When the input is grounded through the switch, the ECM detects the ground signal.The FMI 04 diagnostic code is activated by the ECM when both of the inputs are showing a ground signal at the same time.The conditions that could cause the ECM to activate this diagnostic code are listed below:
The switch has failed.
There is a short to a ground source in one or both of the switch input circuits.
The ECM has failed. This situation is unlikely.Note: Before performing this procedure, inspect the harness connectors that are involved in the circuit. Poor connections can often be the cause of a problem in an electrical circuit. Verify that all connections in the circuit are clean, that all connections are secure, and that all connections are in good condition. If a problem with a connection is found, correct the problem and verify that this diagnostic code is active before performing this procedure.Note: The following test procedure may cause other diagnostic codes to be activated. Ignore these created diagnostic codes and clear the diagnostic codes when the problem has been corrected.Test Step 1. CHECK THE SWITCH
Table 1
Contact States of the Compression Brake Switch
Switch Position Input J2-60 (wire E717-GN(Green)) Input J2-61 (wire E716-GY(Grey))
Compression Brake ON Open(1) Closed(2)
Compression Brake OFF Closed Open
(1) Open to common ground circuit A202-BK.
(2) Closed to common ground circuit A202-BK.
Turn the switch key and the disconnect switch to the OFF position.
Disconnect the machine harness connector from the switch.
With the switch in the ON position, measure the resistance from switch common contact 2 to switch input contact 1. Compare the measurement to the switch contact status table above.
With the switch in the ON position, measure the resistance from switch common contact 2 to switch input contact 3. Compare the measurement to the switch contact status table above.
Move the switch to the OFF position and repeat Steps "C" and "D".Expected Result:The resistance measurements in each switch position agree with the table at the beginning of this test step.Results:
YES - All of the resistance checks for the switch are correct in each switch position according to the table. The switch is working correctly. Proceed to Test Step 2.
NO - The states of the switch are not correct according to the table. The switch has failed.Repair: Replace the compression brake switch. After the switch is replaced, verify that the switch operation is correct before operating the machine.STOPTest Step 2. CHECK THE SWITCH INPUT CIRCUITS FOR A SHORTThe switch key and the disconnect switch remain in the OFF