STUD 9L1657 - Caterpillar

Use this procedure to troubleshoot the electrical system if a problem is suspected with the fuel pump relay or if one of the diagnostic codes in Table 1 is active or easily repeated.
Table 1
Diagnostic Codes Table
J1939 Codes CDL Codes Codes Description System Response
931-5 - Engine Fuel Supply Pump Actuator : Current Below Normal The engine Electronic Control Module (ECM) detects an open circuit at the fuel pump relay for 60 seconds.
The ECM detects a short to battery voltage for the fuel pump relay.
The ECM can only detect this condition when the output driver is not activated.
931-5 - Engine Fuel Supply Pump Actuator : Current Above Normal The engine ECM detects a short circuit for the fuel pump relay.
The ECM can only detect this condition when the output driver is activated. The ECM is able to energize the fuel pump relay. The fuel pump relay controls battery power to the fuel priming pump. The circuit that is for battery power uses a 10 amp fuse for circuit protection. This circuit also provides battery power to the power module that is for the fuel control valve controller.Manually Priming the Fuel SystemA manual switch can be used to prime the fuel system. This switch is used after maintenance has been performed on the fuel system allowing air to be purged from the system without opening up fuel lines. The switch is located near the high-pressure fuel pump on the right side of the engine.When the switch is activated, the ECM powers the electric fuel priming pump. The ECM will command the throttle position for the fuel control valve to 25 percent providing a path for the air. To use this feature, the keyswitch must be in the ON position. Also, the engine speed must be 0 rpm.The switch for the fuel priming pump is a normally open switch.
Illustration 1 g03656723
Typical schematic for the fuel priming pump
Table 2
Troubleshooting Test Steps Values Results
1. Inspect the Electrical Connectors and the Wiring
A. Turn the keyswitch to the OFF position.
B. Inspect the condition of relay . Remove the components from the panel and check for good connections. Thoroughly inspect connectors. Refer to Troubleshooting, "Electrical Connectors - Inspect".
C. Check the torque of the allen head screws for each of the ECM connectors. Refer to Troubleshooting, "Electrical Connectors - Inspect" for the correct torque values.
D. Check the harness and the wiring for abrasion and for pinch points from the connectors for the electric fuel priming pump to the ECM.
Inspect Wiring and Connectors
Results: The connectors and the wiring appear to be OK.
Proceed to Test Step 2.
Results: The connectors and/or the wiring are not OK.
Repair: Repair the connectors and/or the wiring. Replace parts, if necessary.
Verify that the problem is resolved.
2. Check for Active Diagnostic Codes
A. Connect Cat ET to the service tool connector.
B. Restore power to the ECM.
C. Turn the keyswitch to the ON position.
D. Select diagnostic tests from Cat ET.
E. Select the "Override Parameters" screen on Cat ET.
F. Activate the override for the fuel pump relay.
G. Monitor the active diagnostic