IT28G and IT38G Integrated Toolcarriers and 924G, 924GZ, 928G and 938G Wheel Loaders Power Train Electronic Control System Caterpillar

The following diagnostic function should be used if a problem occurs with the load check system but no problems are indicated by the ECM. Possible causes of failure are listed below:

• Faulty wiring to the load check switch

• Loss of power to the ECM

• Incorrect configuration of the options code plug

• Faulty wiring to the load check solenoid

Test Step 1. CHECK THE CONFIGURATION OF THE OPTIONS CODE PLUG

1. Turn the key start switch to the OFF position.

2. Disconnect the machine harness from the ECM.

3. At the machine harness, measure the resistance from contact 2 to the contacts for the option code (28 and 29).

Expected Result:

The resistance at contact 29 should be less than 5 ohms. The resistance at contact 28 should be greater than 5000 ohms.

Results:

• OK - The resistance at contact 29 is less than 5 ohms. The resistance at contact 28 is greater than 5000 ohms. The load check system is correct. Proceed to test step 2.

• NOT OK - The resistance at contact 29 is NOT less than 5 ohms. The resistance at contact 28 is NOT greater than 5000 ohms. The load check system is NOT correct. The option code is not configured correctly.

  Repair: Repair the options code plug or replace the options code plug.

  Stop.

Test Step 2. CHECK CONNECTORS OF THE WIRING HARNESS

1. Disconnect the machine harness from the ECM.

2. Inspect the connectors and inspect the contacts.

3. Connect the machine harness to the ECM.

4. Check the operation of the load check system.

Expected Result:

The load check system operates properly.

Results:

• OK - The load check system operates properly. The problem does not exist at this time. The initial problem 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. Stop.

• NOT OK - The load check system does NOT operate properly. Proceed to test step 3.

Test Step 3. CHECK FOR BATTERY VOLTAGE AT THE ECM

1. Turn the key start switch to the OFF position.

2. Measure the voltage at the battery terminals of the machine.

3. Use the 7X-1710 Multimeter Probe in order to measure the voltage at the harness connector between contacts 1 and 2.

Expected Result:

The voltage at the harness connector does NOT vary from the battery voltage by more than 0.5 VDC.

Results:

• OK - The voltage at the harness connector does NOT vary from the battery voltage by more than 0.5 VDC. The system voltage is correct. Proceed to test step 4.

• NOT OK - The voltage at the harness connector varies from the battery voltage by more than 0.5 VDC.

  Repair: Repair the wiring from the battery to the ECM or replace the wiring from the battery to the ECM.

  Stop.

Test Step 4. CHECK FOR +BATTERY AT THE LOAD CHECK SWITCH

1. Turn the key start switch to the ON position.

2. Measure the voltage at the +battery connection 126-PKto the load check switch.

Expected Result:

The voltage should be +battery.

Results:

• OK - The voltage is +battery. The wiring from the battery to the load check switch is correct. Proceed to test step 5.

• NOT OK - The voltage is NOT +battery. The wiring from the battery to the load check switch is NOT correct.

  Repair: Repair the wiring or replace the wiring.

  Stop.

Test Step 5. CHECK THE LOAD CHECK SWITCH FOR PROPER OPERATION

1. Turn the key start switch to the OFF position.

2. Disconnect the harness connector from the ECM.

3. At the harness connector, measure the resistance from contact 1 to the inputs of the load check switch (contacts 18 and 19).

4. Turn the key start switch to the OFF position.

5. Disconnect the harness connector from the ECM.

6. At the harness connector, measure the resistance from contact 1 to the inputs of the load check switch (contacts 18 and 19).

Expected Result:

The values that were measured should match the values that are listed in table 5.

Results:

• OK - The values that were measured are correct. The switch is correct and the switch harness is correct. Proceed to test step 7.

• NOT OK - The values that were measured are NOT correct. The switch is NOT correct or the switch harness is NOT correct. Proceed to test step 6.

Test Step 6. CHECK THE SWITCH

1. Turn the key start switch to the OFF position.

2. Disconnect the harness connector from the ECM.

3. At the harness connector, measure the resistance from contact 1 to the inputs of the load check switch (contacts 18 and 19).

4. Turn the key start switch to the OFF position.

5. Disconnect the harness connector from the ECM.

6. At the harness connector, measure the resistance from contact 1 to the inputs of the load check switch (contacts 18 and 19).

Expected Result:

The values that were measured should match the values that are listed in table 5.

Results:

• OK - The measured readings are correct. The switch harness is faulty.

  Repair: Repair the harness or replace the harness.

  Proceed to test step 7.

• NOT OK - The measured readings are not correct. The load check switch is faulty.

  Repair: Replace the load check switch.

  Stop.

Test Step 7. TEST THE WIRING FROM THE LOAD CHECK SOLENOID TO GROUND

1. Turn the key start switch to the OFF position.

2. Measure the resistance from the load check relay to the load check solenoid.

Expected Result:

The measured resistance from the load check relay to the load check solenoid is less than 5 ohms.

Results:

• OK - The measured resistance from the load check to the load check solenoid is less than 5 ohms. The wiring is correct. The wiring from the load check solenoid to ground is faulty.

  Repair: Repair the wiring from the load check solenoid to ground or replace the wiring from the load check solenoid to ground.

  Stop.

• NOT OK - The measured resistance from the load check relay to the load check solenoid is NOT less than 5 ohms. The wiring is NOT correct.

  Repair: Repair the wiring from the load check solenoid to the load check relay.

  Stop.