950M and 962M Wheel Loaders Caterpillar


Switch Circuits - Test

Usage:

962M EJB


Implement ECM

The following is a list of Diagnostic Trouble Codes (DTCs) that are associated with the switch circuits of the machine.

Table 1
Implement ECM (MID 82) 
DTC  Description  System Response 
2661-3  Cab Air Temperature Dial: Voltage Above Normal  HVAC system will be non-functional. 
2661-4  Cab Air Temperature Dial: Voltage Below Normal  HVAC system will be non-functional. 
2811-3  Cab Blower Speed Control: Voltage Above Normal  HVAC system will be non-functional. 
2811-4  Cab Blower Speed Control: Voltage Below Normal  HVAC system will be non-functional. 

Possible causes for an FMI 3 Diagnostic code are:

  • The ground wire is open.

  • A signal is permanently open.

  • A short to battery exists in the circuit.

  • The switch has failed.

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

Possible causes for an FMI 4 Diagnostic code are:

  • A short to ground.

  • The switch has failed.

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


Illustration 1g03595437
Schematic of the Switch Circuits

Note: The diagram above is a simplified schematic of the connections for the switch circuits. The schematic is electrically correct. However, not all of the possible harness connectors are shown. Refer to the latest revision of the Electrical Schematic, UENR3117 for the complete schematic.

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. For sensors powered via the fuse panel, check the condition of the appropriate fuse before beginning the troubleshooting procedure.

Table 2
Troubleshooting Test Steps  Values  Results 
1. Identify Active FMI Code Associated With The Switch Circuit 
Code present. 
FMI 3 diagnostic code, proceed to Test Step 2.

FMI 4 diagnostic code, proceed to Test Step 5. 
Begin Process For FMI 3 Troubleshooting HERE 
2. Check The Signal Circuits For An Open

A. Turn the disconnect switch and the key start switch to the OFF position.

B. Disconnect the J1 machine harness connector from the ECM.

C. At the J1 machine harness connector, measure the resistance from the Normally Open contact to the ground contact on the switch with the switch in the normally open position. The switch is pressed.

D. At the J1 machine harness connector, measure the resistance from the Normally Closed contact to the ground contact on the switch with the switch in the normally closed position. The switch is not pressed. 

Open resistance should be greater than 5K ohms. Closed resistance should be less than 5 ohms. The normally open circuit should have open resistance and the normally closed circuit should have closed resistance. These values should reverse when the switch is engaged. 
OK - The measurements are correct.

Proceed to Test Step 3.

NOT OK - One or more of the measurements was incorrect.

Repair: Repair or replace the machine harness.

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

Proceed to Test Step 7. 
3. Check The Resistance Of The Switch

A. Measure the resistance from the normally open contact to the switch return or ground. Toggle the operation of the switch and observe resistance changes.

B. Measure the resistance from the normally closed contact to the switch return or ground. Toggle the operation of the switch and observe resistance changes. 

Open resistance should be greater than 5K ohms. Closed resistance should be less than 5 ohms. The normally open circuit should have open resistance and the normally closed circuit should have closed resistance. These values should reverse when the switch is engaged. 
OK - The measurements are correct.

Proceed to Test Step 4.

NOT OK - One or more of the measurements was incorrect.

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

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

Proceed to Test Step 7. 
4. Check the Ground Circuit Of The Switch In The Harness

A. Turn key start switch and disconnect switch OFF.

B. Disconnect the switch from the machine harness.

C. Measure the resistance between the return contact on the harness to ground. 

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

Proceed to Test Step 5.

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

Repair: Repair or replace the machine harness.

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

Proceed to Test Step 7. 
Begin Process For FMI 4 Troubleshooting HERE 
5. Check The Switch

A. Measure the resistance from the normally open contact to the switch return or ground. Toggle the operation of the switch and observe resistance changes.

B. Measure the resistance from the normally closed contact to the switch return or ground. Toggle the operation of the switch and observe resistance changes. 

Open resistance should be greater than 5K ohms. Closed resistance should be less than 5 ohms. The normally open circuit should have open resistance and the normally closed circuit should have little resistance. These values should reverse when the switch is engaged. 
OK - The measurements are correct.

Proceed to Test Step 6.

NOT OK - One or more of the measurements was incorrect.

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

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

Proceed to Test Step 7. 
6. Check The Signal Circuits For An Open

A. Reconnect the switch to the machine harness.

B. Repeat Test Step 7, however instead of measuring the resistance from the switch contacts, measure from the corresponding contacts on the ECM harness. 

Open resistance should be greater than 5K ohms. Closed resistance should be less than 5 ohms. The normally open circuit should have open resistance and the normally closed circuit should have closed resistance. These values should reverse when the switch is engaged. 
OK - The measurements are correct.

Proceed to Test Step 7.

NOT OK - One or more of the measurements was incorrect.

Repair: Repair or replace the machine harness.

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

Proceed to Test Step 7. 
7. 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 Caterpillar. 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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