3126B Engine for Caterpillar Built Machines Caterpillar

The fuel pump supplies fuel to the unit injector hydraulic pump. The fuel pump is also used to prime the fuel lines if the engine runs out of fuel and the fuel pump is used to prime the fuel lines after changing the fuel filters. Use the following information to check the operation of the relay for the fuel pump.

Note: Check the fuel level before performing any fuel pump tests. Damage to the fuel pump could occur if there is no fuel in the fuel tank.

Illustration 1	g00883575
Schematic for the relay of the fuel pump

Illustration 2	g00883653
Terminal locations for the ECM connector P1

Test Step 1. Inspect Electrical Connectors and Wiring

1. Turn the keyswitch to the OFF/RESET position.

2. Thoroughly inspect the J1/P1 ECM connector and all other connectors in the circuit. Refer to Troubleshooting, "Electrical Connectors-Inspect" for details.

3. Perform a 45 N (10 lb) pull test on all the wires that are associated with the circuit for the fuel pump.

4. Check the ECM connector (allen head screw) for the proper torque of 6.0 N·m (55 lb in).

5. Check the harness and wiring for abrasion and for pinch points from the sensors back to the ECM.

Expected Result:

All connectors, pins and sockets should be completely coupled and/or inserted and the harness and wiring should be free of corrosion, abrasion or pinch points.

Results:

• OK - The connectors and the wiring is good. Proceed to Test Step 2.

• Not OK - There is a problem with the connectors and the wiring.

  Repair: Perform the following repair:Repair the connectors or wiring and/or replace the connectors or wiring. Ensure that all of the seals are properly in place and ensure that the connectors are completely coupled.Verify that the repair eliminates the problem.

  STOP

Test Step 2. Perform the "Fuel Pump Relay Command Override"

1. Turn the keyswitch to the OFF/RESET position.

2. Connect the Caterpillar Electronic Technician (Cat ET) to the service tool connector.

3. Turn the keyswitch to the ON position.

4. Go to the "Fuel Pump Relay Command Override" on Cat ET.

5. Start the test and listen for a click from the relay for the fuel pump.

   Note: Do not leave the "Fuel Pump Relay Command Override" on. Avoid unnecessary cycling of the fuel pump in order to prevent the battery from discharging. The fuel pump has a 120 second timer in order to disable the test when the time expires.

Expected Result:

The relay activates when the "Fuel Pump Relay Command Override" is turned on.

Results:

• OK - The relay is working properly. Proceed to Test Step 3.

• Not OK - There is a problem with the relay circuit. Proceed to Test Step 6.

Test Step 3. Check the Voltage Output at the Relay

Illustration 3	g00883663

1. Turn the keyswitch to the OFF/RESET position.

2. Disconnect the wire from terminal 4 (Fuel Pump) on the relay connector.

3. Connect a voltage test lamp between the disconnected relay terminal and chassis ground.

4. Turn the keyswitch to the ON position.

5. Go to the "Fuel Pump Relay Command Override" on Cat ET.

6. Start the test and watch the voltage test lamp.

   Note: Do not leave the "Fuel Pump Relay Command Override" on. Avoid unnecessary cycling of the fuel pump in order to prevent the battery from discharging. The fuel pump has a 120 second timer in order to disable the test when the time expires.

Expected Result:

The test lamp turned on and the test lamp turned off with the "Fuel Pump Relay Command Override".

Results:

• OK - The relay for the fuel pump and the +battery connection to the relay for the fuel pump are OK. Reconnect the wire from the fuel pump to the terminal on the relay for the fuel pump. Proceed to Test Step 4.

• Not OK - The test lamp does not turn on or the test lamp stays on. Reconnect the wire from the fuel pump to the terminal on the relay for the fuel pump. Proceed to Test Step 9.

Test Step 4. Check the Resistance of the Fuel Pump

1. Disconnect the connector for the fuel pump.

2. Measure the resistance of the fuel pump.

3. Reconnect the connector for the fuel pump.

Expected Result:

Resistance should be less than 10 Ohms.

Results:

• OK - The resistance of the fuel pump is OK. Proceed to Test Step 5.

• Not OK - The resistance of the pump is out of specification.

  Repair: Replace the fuel pump.Verify that the repair eliminates the problem.

  STOP

Test Step 5. Check the Supply Voltage to the Fuel Pump

Illustration 4	g00883621

1. Disconnect the fuel pump.

2. Turn the keyswitch to the ON position.

3. Proceed to the "Fuel Pump Relay Command Override" on Cat ET.

4. Activate the relay for the fuel pump.

   Note: The diagnostic override will only activate the relay for 120 seconds.

5. Use signal reading probes to measure the voltage across terminal 1 (Signal) and terminal 2 (Ground) of the connector for the fuel pump.

Expected Result:

The supply voltage should be greater than 22.0 VDC.

Results:

• OK - The relay is supplying the proper signal to the fuel pump, but the fuel pump is not working.

  Repair: Replace the fuel pump.Verify that the repair eliminates the problem.

  STOP

• Not OK - The fuel pump is not receiving the correct signal. Proceed to Test Step 6.

Test Step 6. Check the Resistance of the Relay

Illustration 5	g00883651
Relay Terminals

1. Turn the keyswitch to the OFF/RESET position.

2. Unplug the relay for the fuel pump.

3. Measure the resistance between terminal 86 (Fuel Pump Relay (Signal)) and terminal 85 (Solenoid Return) of the relay.

Expected Result:

The resistance should be between 250 Ohms and 500 Ohms.

Results:

• OK - The resistance is between 250 Ohms and 500 Ohms. Proceed to Test Step 7.

• Not OK - The relay is faulty.

  Repair: Replace the relay.Verify that the repair eliminates the problem.

  STOP

Test Step 7. Check the Signal Voltage to the Relay

Illustration 6	g00883664

1. Unplug the relay for the fuel pump.

2. Turn the keyswitch to the ON position.

3. Proceed to the "Diagnostic Overrides" screen on Cat ET.

4. Activate the system for the fuel pump.

   Note: The diagnostic override will only activate the relay for 120 seconds.

5. Measure the voltage between terminal 2 (Solenoid Return) and terminal 5 (Fuel Pump Relay (Signal)) of the plug for the relay.

Expected Result:

The voltage should be 24.0 ± 8.0 VDC.

Results:

• OK - The relay is receiving the signal from the ECM. Proceed to Test Step 8.

• Not OK - The relay is not receiving the signal from the ECM. Proceed to Test Step 10.

Test Step 8. Check the Output Voltage of the Relay

Illustration 7	g00883663

1. Ensure that all connectors are connected to the wiring harness.

2. Turn the keyswitch to the ON position.

3. Proceed to the "Diagnostic Overrides" screen on Cat ET.

4. Activate the system for the fuel pump.

   Note: The diagnostic override will only activate the relay for 120 seconds.

5. Use signal reading probes to measure the voltage across terminal 4 (Fuel Pump Power) of the relay and chassis ground.

Expected Result:

The voltage should be 24.0 ± 8.0 VDC.

Results:

• OK - There is a problem in the wiring between the relay and the fuel pump.

  Repair: Repair the circuit.Verify that the repair eliminates the problem.

  STOP

• Not OK - The relay is not sending power to the fuel pump. Proceed to Test Step 9.

Test Step 9. Check the Power Supply to the Relay

Illustration 8	g00883664

1. Unplug the fuel pump.

2. Measure the voltage between terminal 1 (+Battery) of the connector for the relay and chassis ground.

Expected Result:

The voltage should be 24.0 ± 8.0 VDC.

Results:

• OK - The relay is faulty.

  Repair: Replace the relay.Verify that the repair eliminates the problem.

  STOP

• Not OK - There is a problem in the wiring between the relay and the +Battery terminal.

  Repair: Repair the circuit.Verify that the repair eliminates the problem.

  STOP

Test Step 10. Check for Shorts in the Wiring Harness between the Relay and the ECM

1. Ensure that the keyswitch is in the OFF/RESET position.

2. Disconnect the J1/P1 ECM connector.

3. Unplug the relay for the fuel pump.

4. Measure the resistance between P1:19 (Fuel Pump Relay (Signal)) and P1:67 (Solenoid Return).

Expected Result:

The resistance should be greater than 20,000 Ohms.

Results:

• OK - The resistance is greater than 20,000 Ohms. Proceed to Test Step 11.

• Not OK - There is a short between the ECM and the relay.

  Repair: Repair the circuit.Verify that the repair eliminates the problem.

  STOP

Test Step 11. Check the Voltage for the Relay at the ECM

1. Turn the keyswitch to the OFF/RESET position.

2. Remove the wire from P1:19 (Fuel Pump Relay) and P1:67 (Solenoid Return) in the P1 ECM connector.

3. Turn the keyswitch to the ON position.

4. Proceed to the "Fuel Pump Relay Command Override" on Cat ET.

5. Activate the system for the fuel pump.

   Note: The diagnostic override will only activate the relay for 120 seconds.

6. Measure the voltage between the open terminal at P1:19 (Fuel Pump Relay) and P1:67 (Solenoid Return).

7. Turn the keyswitch to the OFF/RESET position.

8. Reinstall the wire to P1:19 (Fuel Pump Relay) and P1:67 (Solenoid Return).

Expected Result:

The voltage should be 24.0 ± 8.0 VDC.

Results:

• OK - The ECM is supplying the correct voltage. There may be an open circuit or a short circuit in the harness.

  Repair: Repair the circuit.Verify that the repair eliminates the problem.

  STOP

• Not OK - The ECM is not supplying the correct voltage.

  Repair: Verify your results. Replace the ECM. Refer to Troubleshooting, "Replacing the ECM" before replacing the ECM.Verify that the repair eliminates the problem.

  STOP