906K, 906M, 907K, 907M, 908K and 908M Compact Wheel Loaders Electrohydraulic System Operator Control Switch (Switch to Ground) - Test Caterpillar


Operator Control Switch (Switch to Ground) - Test
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1.1. Machine ECM
2.1. Diagnostic Trouble Code Procedure

Machine ECM

The following is a list of Diagnostic Trouble Codes (DTCs) that are associated with the Operator Control Switch to ground of the machine.

Table 1
Machine ECM (MID 71) 
DTC  Code Description  System Response 
70-3  Parking Brake Switch: Voltage above normal  The parking brake lever may not correspond with the parking brake indicator on the display. 
70-4  Parking Brake Switch: Voltage below normal  The parking brake lever may not correspond with the parking brake indicator on the display. 
490-3  Implement Lockout Switch: Voltage above normal  Implements cannot be locked out. Some machine calibrations cannot be performed. 
490-4  Implement Lockout Switch: Voltage below normal  Implements cannot be locked out. Some machine calibrations cannot be performed. 
584-2  Engine Oil Pressure Switch: Data erratic, intermittent, or incorrect  Machine will operate as normal. However, engine oil pressure monitoring is disabled. 
2274-2  Direction Selector #2: Data erratic, intermittent, or incorrect  The transmission will neutralize. 
1529-4  Quick Coupler Switch: Voltage below normal  Quick Coupler feature is disabled. 
4403-4  Gear Range Switch: Voltage below normal  Some hystat speed ranges are not selectable. 

Possible causes for an FMI 2 diagnostic code are:

  • A short circuit exists.

  • An open circuit exists.

  • The switch has failed.

  • The ECM has failed. A failure of the ECM is unlikely.

Possible causes for an FMI 3 diagnostic code are:

  • The sensor supply or the ground circuit in the machine harness is open.

  • The signal circuit in the machine harness is shorted to another circuit.

  • The signal circuit in the machine harness is open or the sensor is disconnected.

  • The sensor has failed.

  • The ECM has failed. An ECM failure is unlikely.

Possible causes for an FMI 4 diagnostic code are:

  • The signal circuit in the machine harness is shorted to ground.

  • The sensor has failed.

  • The ECM has failed. An ECM failure is unlikely.


Illustration 1g03814503
Schematic of the Switch to Ground

Note: The diagram above is a simplified schematic of the Machine ECM and the Switch to Ground connections. The schematic is electrically correct. However, not all of the possible harness connectors are shown. Refer to the latest revision of Electrical Schematic, UENR5407 for prefixes: L66, L77, L88, or Electrical Schematic, UENR5408 for prefixes: Z66, Z77, Z88, or Electrical Schematic, UENR5409 for prefixes: H66, H77, H88

Diagnostic Trouble Code Procedure

Note: Prior to beginning this procedure, inspect the harness connectors that are involved in this circuit. Poor connections can often be the cause of a problem in an electrical circuit. Verify that all connections in the circuit are clean, secure, and in good condition. If a problem with a connection is found, correct the problem and verify that the diagnostic code is active before performing a troubleshooting procedure.

Table 2
Troubleshooting Test Steps  Values  Results 
1. Identify Active FMI Code Associated With Sensor Circuit 
Code present. 
FMI 2 diagnostic code, proceed to Test Step 2.

FMI 3 diagnostic code, proceed to Test Step 4.

FMI 4 diagnostic code, proceed to Test Step 8. 
Begin Process For FMI 2 Troubleshooting HERE 
2. Check The Circuit For A Short

A. Turn the keyswitch OFF.

B. Disconnect the switch from the machine harness.

C. Disconnect the J1 and J2 machine harness connections from the ECM.

D. At the machine harness connector for the ECM, one at a time, measure the resistance between each of the signal contacts to every other contact used in the J1 and J2 machine harness connectors. 

The resistance is greater than 5K Ω. 
OK - The resistance is correct.

Proceed to Test Step 3.

NOT OK - The resistance check is not correct.

Repair: There is a short in the signal circuits of the machine harness. Repair or replace the machine harness.

Proceed to Test Step 12. 
3. Check the Operation of the Switch.

A. The keyswitch remains OFF.

B. Reconnect all harness connectors.

C. Check the operation of the switch. Refer to the table for the suspected faulty switch at the beginning of this procedure for switch operation. 

The switch operates correctly. 
OK - The switch is operating correctly.

Proceed to Test Step 12.

NOT OK - The switch is not operating correctly. The switch has failed

Repair: Replace the switch.

Proceed to Test Step 12. 
Begin Process For FMI 3 Troubleshooting HERE 
4. Check the Harness For an Open

A. Turn key start switch and disconnect switch OFF.

B. Disconnect the switch from the machine harness.

C. Disconnect the J1 and J2 machine harness connector.

D. At the machine harness connector for the switch, place a jumper wire between the signal contact and frame ground.

E. At the machine harness connect for the ECM, measure the resistance between the signal contact and frame ground. 

The resistance is less than 5 Ω. 
OK - The circuit is correct.

Proceed to Test Step 5.

NOT OK - The resistance is greater than 5K Ω. The circuit is open.

Repair: Repair or replace the machine harness.

Note: A resistance that is greater than 5 Ω but less than 5K Ω indicates a loose connection or a corroded connection in the circuit. A resistance measurement that is greater than 5K Ω indicates an open in the circuit.

Proceed to Test Step 12. 
5. Check the Harness for a Short

A. The keyswitch remains OFF.

B. All harness connectors remain disconnected.

C. Remove the jumper wire installed in the previous step.

D. At the machine harness connector for the ECM, measure resistance between the signal contact and all other contacts used in the J1 and J2 harness connectors. 

The resistances are greater than 5K Ω. 
OK - The resistance is greater than 5K Ω. The harness circuit is correct.

Proceed to Test Step 6.

NOT OK- The resistance less than 5 Ω.

Repair: A short exists in the harness between the signal circuit and the wire with the low resistance reading. Repair or replace the machine harness.

Note: A resistance that is greater than 5 Ω but less than 5K Ω would indicate a loose connection or a corroded connection in the circuit. A resistance measurement that is greater than 5K Ω would indicate an open in the circuit.

Proceed to Test Step 12. 
6. Check the Ground Source for the Switch.

A. The keyswitch remains OFF.

B. All harness connectors remain disconnected.

C. At the switch, measure resistance between the ground contact and frame ground. 

The resistance is less than 5 Ω. 
OK - The resistance is less than 5 Ω.

Proceed to Test Step 7.

NOT OK - The resistance is greater than 5K Ω.

Repair: The switch does not have a good ground source. Replace the harness between the switch and the ground source.

Note: A resistance that is greater than 5 Ω but less than 5K Ω indicates a loose connection or a corroded connection in the circuit. A resistance measurement that is greater than 5K Ω indicates an open in the circuit.

Proceed to Test Step 12. 
7. Check the Operation of the ECM.

A. The keyswitch remains OFF.

B. Reconnect all harness connections.

C. Using a wire removal tool, remove the signal wire and socket from the machine harness connector to the ECM.

D. Turn the keyswitch ON.

E. Use a multimeter probe to make contact with the ECM pin through the empty space in the harness connector.

F. Ground the other end of the multimeter probe to frame ground.

G.Observe the status of the diagnostic code. 

The FMI 3 changes to an FMI 4. 
OK - The ECM is operating correctly.

Proceed to Test Step 8.

NOT OK - The FMI 3 remains. The ECM may have failed.

Prior to replacing the ECM, always contact the Technical Communicator at your dealership for possible consultation with AVSpare. This consultation may greatly reduce repair time.

If the ECM requires replacement, see Troubleshooting, "ECM - Replace"

Proceed to Test Step 12. 
8. Check the Operation of the Switch.

A. Turn the keyswitch OFF.

B. Reinstall the signal wire removed in the previous step.

C. Check the operation of the switch. Refer to the table for the suspected faulty switch at the beginning of this procedure for switch operation. 

The switch operates correctly. 
OK - The switch is operating correctly.

Proceed to Test Step 12.

NOT OK - The switch is not operating correctly. The switch has failed

Repair: Replace the switch.

Proceed to Test Step 12. 
Begin Process For FMI 4 Troubleshooting HERE 
9. Check The Switch

A. Turn the keyswitch OFF.

B. Unplug the switch.

C. Turn the keyswitch ON.

D. Observe the status of the diagnostic code. 

The FMI 4 diagnostic code remains active. 
OK - The FMI 4 diagnostic code remains active.

Proceed to Test Step 10.

NOT OK - The FMI 4 changes to an FMI 3. The switch has failed.

Repair: Replace the switch. Verity that the new switch corrects the diagnostic code.

Proceed to Test Step 12. 
10. Check the Harness for a Short

A. The keyswitch remains OFF.

B. Unplug the J1 and J2 machine harness connectors form the ECM.

C. At the machine harness connector for the ECM, measure resistance between the signal contact and all other contacts used in the J1 and J2 harness connectors. 

The resistances are greater than 5 K Ω. 
OK - The resistance is greater than 5K Ω. The harness circuit is correct.

Proceed to Test Step 11.

NOT OK- The resistance less than 5 Ω.

Repair: A short exists in the harness between the signal circuit and the wire with the low resistance reading. Repair or replace the machine harness.

Note: A resistance that is greater than 5 Ω but less than 5K Ω would indicate a loose connection or a corroded connection in the circuit. A resistance measurement that is greater than 5K Ω would indicate an open in the circuit.

Proceed to Test Step 12. 
11. Check the Operation of the Switch.

A. The keyswitch remains OFF.

B. Check the operation of the switch. Refer to the table for the suspected faulty switch at the beginning of this procedure for switch operation. 

The switch operates correctly. 
OK - The switch is operating correctly.

Proceed to Test Step 12.

NOT OK - The switch is not operating correctly. The switch has failed

Repair: Replace the switch.

Proceed to Test Step 12. 
12. Check If The Diagnostic Code Remains

A. Inspect the harness connectors and clean the contacts of the harness connectors.

B. Perform a 45 N (10 lb) pull test on each of the wires that are associated with the circuit.

B. Reconnect all harness connectors.

C. Turn key start switch and disconnect switch ON.

D. Operate the machine.

Check the status of the diagnostic code. 

The diagnostic code is not active. 
OK - The diagnostic code is still active.

Repair: Check the status of the diagnostic code. If the cause of the problem is not found, the ECM may require replacement.

Prior to replacing the ECM, always contact the Technical Communicator at your dealership for possible consultation with AVSpare. This consultation may greatly reduce repair time.

If the ECM requires replacement, see Troubleshooting, "ECM - Replace"

STOP

NOT OK - The continuity check is not correct.

Repair: There is an open in the signal circuits of the machine harness. Repair or replace the machine harness.

STOP 

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