CB-634D Paving Compactor Machine Electronic Control System Caterpillar

If the backup alarm is always ON, one of the following conditions exists:

• There is a problem with the relay for the backup alarm.

• The harness circuit is shorted to the +battery circuit.

• The ECM has failed.

Note: Ensure that the backup alarm is ON before performing this procedure.

Illustration 1	g00904563

Test Step 1. CHECK THE HARNESS.

1. Remove the backup alarm relay.

2. Turn the key start switch and the disconnect switch to the ON position.

Expected Result:

The backup alarm is OFF.

Results:

• YES - The backup alarm is OFF. Go to Test Step 2.

• NO - The backup alarm continues to sound. Reinstall the backup alarm relay. Go to Test Step 4.

Test Step 2. CHECK THE BACKUP ALARM RELAY.

1. Turn OFF the key start switch and the disconnect switch.

2. At the backup alarm relay, remove the signal wire to the backup alarm relay (contact 2).

3. Reinstall the backup alarm relay.

4. Turn ON the key start switch and the disconnect switch.

Expected Result:

The backup alarm is not active.

Results:

• OK - The backup alarm is not active. Reconnect the signal wire to the alarm relay (contact 2). Go to Test Step 3.

• NOT OK - The backup alarm is active. The backup alarm relay has failed.

  Repair: The backup alarm relay has failed. Replace the backup alarm relay.

  Stop.

Test Step 3. CHECK THE SIGNAL OF THE SENSOR.

1. Replace the signal wire in that was removed in the previous step.

2. At the back of the harness connector for the sensor, insert the probe of the 7X-1710 Multimeter Probe along the signal wire (contact 3).

3. At the back of the harness connector for the sensor, insert the other 7X-1710 Multimeter Probe along the ground wire (contact 2).

4. Turn the disconnect switch and the key start switch to the ON position.

5. Monitor the signal of the sensor with the 146-4080 Digital Multimeter .

6. Move the joystick to the NEUTRAL position. Check the signal. The signal should be operating at a 50% duty cycle.

7. Move the joystick slowly forward. Check the signal.

Expected Result:

The value for the duty cycle rises above 50%.

Results:

• OK - The value for the duty cycle rises above 50%. The backup alarm goes OFF. Go to Test Step 6.

• NOT OK - The value of the duty cycle is above 48%, and the backup alarm does not go OFF. The ECM has failed.

  Repair: It is unlikely that the ECM has failed. Exit this procedure and perform this procedure again. If the cause of the failure is not found, replace the ECM.

  Stop.

• NOT OK - The duty cycle remains less than 48%.

  Repair: Replace the sensor. Verify that the replacement of the sensor corrects the problem.

  Stop.

Test Step 4. CHECK THE HARNESS TO THE BACKUP ALARM RELAY FOR A SHORT TO THE +BATTERY CIRCUIT.

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

2. Disconnect the machine harness connector from the ECM.

3. Remove the backup alarm relay.

4. Measure the resistance between contact 17 on the ECM, wire (C936 GY-18) and all contacts that are used in the machine harness connector for the ECM.

Expected Result:

Each of the resistance measurements are greater than 5000 Ohms.

Results:

• OK - The circuit is correct. Go to Test Step 5

• NOT OK - The resistance is less than 5000 Ohms. The signal circuit is shorted to another circuit in the harness.

  Repair: Repair the machine harness or replace the machine harness.

  Stop.

Test Step 5. CHECK THE POWER CIRCUIT FOR THE RELAY TO THE BACKUP ALARM.

1. The key start switch and the disconnect switch remain in the OFF position. The relay remains removed.

2. Measure the resistance at the backup alarm between the power circuit, wire (321 BR-18) and all contacts that are used in the machine harness connectors for the ECM.

Expected Result:

Each of the resistance measurements are greater than 5000 Ohms.

Results:

• OK - The circuit is correct. Go to Test Step 6.

• NOT OK - The resistance is less than 5000 Ohms. The signal circuit is shorted to another circuit in the harness.

  Repair: Repair the machine harness or replace the machine harness.

  Stop.

Test Step 6. CHECK IF THE PROBLEM REMAINS.

1. Inspect the harness connectors and clean the contacts of the machine harness connectors.

2. Reconnect all harness connectors.

3. Turn the disconnect switch and the key start switch to the ON position.

4. Operate the machine and operate the sensor through the operating range of the sensor.

5. Check if the backup alarm is still active.

Expected Result:

The backup alarm is not active.

Results:

• OK - The backup alarm is not active. The problem was probably caused by a poor connection or a short at one of the connectors that was disconnected and reconnected. Resume normal operation. Stop.

• NOT OK - The backup alarm is still active. Exit this procedure. Perform this procedure again. Stop.