Conditions Which Generate This Code:
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
|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".
The resistance measurements in each switch position agree with the table at the beginning of this test step.
- 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.
Test Step 2. CHECK THE SWITCH INPUT CIRCUITS FOR A SHORT
The switch key and the disconnect switch remain in the OFF position. The machine harness remains disconnected from the switch.
- Disconnect the machine harness connectors J1 and J2 from the ECM.
- At the machine harness connector J2 for the ECM, measure the resistance between switch input contact J2-61 (wire E716-GY(Grey)) and frame ground. Measure the resistance between switch input contact J2-61 (wire E716-GY(Grey)) and all the other contacts that are used in the J1 and J2 harness connectors for the ECM.
- At the machine harness connector J2 for the ECM, measure the resistance between switch input contact J2-60 (wire E717-GN(Green)) and frame ground. Measure the resistance between switch input contact J2-60 (wire E717-GN(Green)) and all the other contacts that are used in the J1 and J2 harness connectors for the ECM.
Each resistance measurement is greater than 5000 ohms.
- OK - Each resistance measurement is greater than 5000 ohms. The inputs of the switch circuits are not shorted to ground or to another circuit in the machine harness. Proceed to Test Step 3.
- NOT OK - One or more of the resistance measurements are less than 5000 ohms. There is a short to ground or to another circuit in the machine harness.
Repair: The input circuit that checks the low resistance to frame ground or to another circuit is causing the problem.
Refer to the complete Electrical System Schematic of the machine. Check all the connectors that are in the suspect input circuit. Ensure that all connections are clean, that all connections are secure, and that all connections are in good condition.
For information on testing for short circuits and finding short circuits, refer to Testing and Adjusting, "Wiring Harness (Short Circuit) - Test". Repair the machine harness or replace the machine harness.
Test Step 3. CHECK THE STATUS OF THE DIAGNOSTIC CODE
- Inspect the harness connectors. Clean the contacts of the harness connectors. Check the wires for damage to the insulation that is caused by excessive heat, corrosion, or chafing.
- Perform a
45 N (10 lb)pull test on each of the wires that are associated with the sensor circuit.
- Reconnect all harness connectors. Make sure that the connectors are fully seated. Observe that the clips for each connector are fastened.
- Turn the disconnect switch and the key start switch to the ON position.
- Operate the machine.
- Check the status of the CID 2734 FMI 04 diagnostic code.
The CID 2734 FMI 04 diagnostic code is active.
- YES - The CID 2734 FMI 04 diagnostic code is active. The diagnostic code has not been corrected.
Repair: Check the input circuits of the switch again. Use the AVSpare Electronic Technician (ET) service tool to perform a wiggle test on the machine wiring harness. The wiggle test can detect momentary or intermittent shorts or opens in the machine wiring harness.
If the cause can not be found, the ECM may have failed. Verify that all possible causes of the diagnostic code have been investigated before replacement of the ECM.
Prior to replacing an ECM, always contact your dealership's Technical Communicator for possible consultation with AVSpare. This consultation may greatly reduce repair time. If the cause of the diagnostic code is not found, replace the ECM. Refer to Testing and Adjusting, "Electronic Control Module (ECM) - Replace".
- NO - The CID 2734 FMI 04 is not active. The diagnostic code does not exist at this time.
Repair: The initial diagnostic code was probably caused by a poor electrical connection or a short at one of the harness connectors that was disconnected and reconnected. Resume normal machine operation.