C175-16 Petroleum Engine Caterpillar

Use this procedure to troubleshoot the electrical system if a problem is suspected with the fuel pump relay. Also, use this procedure if one of the diagnostic codes in Table 1 is active or easily repeated.

Table 1

J1939 Code and Description	CDL Code and Description	System Response
931-5 Engine Fuel Supply Pump Actuator : Current Below Normal	1627-5 Fuel Pump Relay current below normal	The 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 for 60 seconds. The ECM can only detect this condition when the output driver is not activated. The code is logged.
931-6 Engine Fuel Supply Pump Actuator : Current Above Normal	1627-6 Fuel Pump Relay current above normal	The ECM detects a short circuit for the fuel pump relay. The ECM can only detect this condition when the output driver is activated. The code is logged.

During the following scenarios ECM energizes the fuel pump relay. The fuel pump relay controls battery power to the fuel priming pump.

ECM Activation of the Fuel Priming Pump

This strategy improves the capability of the fuel system at low engine speeds.

The ECM will automatically activate the fuel priming pump while the engine state is CRANKING, RUNNING, or POSTRUN. The ECM deactivates the fuel pump when the engine speed is greater than 200 rpm.

Manual Override of the Fuel Priming Pump

Use the "Fuel Priming Pump Command Override" in Cat^® Electronic Technician (ET) to diagnose a problem with the electric fuel priming pump. A "Fuel Priming Pump Command" parameter is also available in Cat ET that can be used to view the status of the ECM output.

When the override is activated, the ECM powers the electric fuel priming pump. The ECM will command the FCV throttle position to 25 percent. Opening the FCV throttle provides a path for air to escape from the low-pressure fuel system. To use this feature, the ECM and the keyswitch relay must be powered. Also, the engine speed must be 0 rpm.

Illustration 1	g02783247
Schematic for the electric fuel priming pump (control assembly input connectors) if equipped with an A4 ECM

Illustration 2	g06320834
Schematic for the electric fuel priming pump (control assembly input connectors) if equipped with an A5 ECM

Illustration 3	g02783249
Schematic for the electric fuel priming pump (control assembly output connector) if equipped with an A4 ECM

Illustration 4	g06328492
Schematic for the electric fuel priming pump (control assembly output connector) if equipped with an A5 ECM

Table 2

Troubleshooting Test Steps	Values	Results
1. Inspect the Electrical Connectors and the Wiring A. Turn the battery disconnect switch to the OFF position. B. Thoroughly inspect the electrical connectors and breakers. Reset the breaker, if necessary. 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 fuel priming pump to the ECM.	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 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. Turn the battery disconnect switch to ON. C. Select diagnostic tests from Cat ET. D. Select the "Override Parameters" screen on Cat ET. E. Activate the override for the fuel pump relay. F. Monitor the active diagnostic code screen on Cat ET. Check and record any active diagnostic codes for the fuel priming pump. Note: Wait at least 30 seconds in order for the diagnostic code to become active. G. Deactivate the override for the fuel pump relay. H. Monitor the active diagnostic code screen on Cat ET. Check and record any active diagnostic codes. Note: Wait at least 30 seconds in order for the diagnostic codes to become active. I. Turn the battery disconnect switch to OFF.	Codes	Results: No diagnostic codes are active, but a problem is suspected in the circuit for the fuel priming pump. Proceed to Test Step 7 Results: A -6 diagnostic code is active currently. Proceed to Test Step 3 Results: A -5 diagnostic code is active currently. Proceed to Test Step 4
3. Create an Open at the Connector for the Fuel Pump Relay A. Disconnect the connector from the fuel pump relay. B. Turn the battery disconnect switch to ON. C. Select diagnostic tests from Cat ET. D. Select the "Override Parameters" screen on Cat ET. E. Activate the override for the fuel pump relay. F. Monitor the active diagnostic code screen on Cat ET. Check and record any active diagnostic codes. Note: Wait at least 30 seconds in order for the diagnostic code to become active. G. Deactivate the override for the fuel pump relay. H. Monitor the active diagnostic code screen on Cat ET. Check and record any active diagnostic codes. Note: Wait at least 30 seconds in order for the diagnostic codes to become active. I. Turn the battery disconnect switch to OFF.	Open Circuit or -5 Code	Results: A -5 diagnostic code became active after disconnecting the connector for the fuel priming pump. Repair: Temporarily install a new fuel pump relay. Verify that there are no active diagnostic codes for the fuel pump relay. Clear any logged diagnostic codes. Results: A -6 diagnostic code remains active. There is a short between the connector for the fuel pump relay and the ECM. Proceed to Test Step 5
4. Create a Short at the Connector for the Fuel Pump Relay A. Disconnect the connector for the fuel pump relay. Install a jumper wire between the terminals at the connector for the fuel pump relay. Refer to Illustration 3 for the schematic of the circuit. B. Turn the battery disconnect switch to ON. C. Select diagnostic tests from Cat ET. D. Select the "Override Parameters" screen on Cat ET. E. Activate the override for the fuel pump relay. F. Monitor the active diagnostic code screen on Cat ET. Check and record any active diagnostic codes. Note: Wait at least 30 seconds in order for the diagnostic code to become active. G. Deactivate the override for the fuel pump relay. H. Monitor the active diagnostic code screen on Cat ET. Check and record any active diagnostic codes. Note: Wait at least 30 seconds in order for the diagnostic codes to become active. I. Turn the battery disconnect switch to the OFF position.	Short Circuit or -6 Code	Results: The engine harness and the ECM are OK. Repair: Temporarily install a new fuel pump relay. Verify that there are no active diagnostic codes for the fuel pump relay. Clear any logged diagnostic codes. Results: The -5 diagnostic code remains active with the jumper in place. Verify that the wire at terminal 2 of the connector for the fuel pump relay has continuity to the −Battery. If the return circuit is OK, the open circuit is between the ECM and the connector for the fuel pump relay. Proceed to Test Step 6
5. Check the operation of the ECM by creating an open at the ECM connector: A. Disconnect the J1/P1 ECM connector. B. Remove the wire for the fuel pump relay from P1-10. C. Install a wire jumper into the socket for P1-10. Ensure that the wire jumper is not in contact with any other wire in the harness or in contact with engine ground. D. Reconnect the ECM connector. E. Turn the battery disconnect switch to ON. F. Select diagnostic tests from Cat ET. G. Select the "Override Parameters" screen on Cat ET. H. Activate the override for the fuel pump relay. I. Monitor the active diagnostic code screen on Cat ET. Check and record any active diagnostic codes. Note: Wait at least 30 seconds in order for the diagnostic code to become active. J. Deactivate the override for the fuel pump relay. K. Monitor the active diagnostic code screen on Cat ET. Check and record any active diagnostic codes. Note: Wait at least 70 seconds in order for the diagnostic codes to become active. L. Turn the keyswitch to OFF. J. Restore the wiring to the original configuration.	ECM	Results: The ECM is operating properly. The problem is in the wiring between the ECM and the connector for the fuel pump relay. Repair: Repair the connectors or wiring and/or replace the connectors or wiring. Results: One of the following conditions exists: The -5 diagnostic code is not active when the wire jumper is open. The -6 diagnostic code is not active when the wire jumper is connected to the −Battery. Repair: There is a problem with the ECM. Perform the following procedure: 1. Temporarily connect a test ECM. Refer to Troubleshooting, "ECM - Replace" 2. Recheck the circuit to ensure that the original problem has been resolved. If the problem is resolved with the test ECM, install the suspect ECM. Before you consider replacing the ECM, consult the Dealer Solutions Network (DSN) for assistance. If the problem is not resolved with the test ECM, install the original ECM. There is a problem in the wiring.
6. Check the operation of the ECM by creating a short circuit at the ECM connector: A. Install a wire jumper between the jumper wire in P1-10 and the −Battery. B. Turn the battery disconnect switch to ON. C. Select diagnostic tests from Cat ET. D. Select the "Override Parameters" screen on Cat ET. E. Activate the override for the fuel pump relay. F. Monitor the active diagnostic code screen on Cat ET. Check and record any active diagnostic codes. Note: Wait at least 30 seconds in order for the diagnostic code to become active. G. Deactivate the override for the fuel pump relay. H. Monitor the active diagnostic code screen on Cat ET. Check and record any active diagnostic codes. Note: Wait at least 70 seconds in order for the diagnostic codes to become active. I. Turn the battery disconnect switch to OFF. J. Restore the wiring to the original configuration.	ECM	Results: The ECM is operating properly. The problem is in the wiring between the ECM and the connector for the fuel pump relay. Repair: Repair the connectors or wiring and/or replace the connectors or wiring. Results: One of the following conditions exists: The -5 diagnostic code is not active when the wire jumper is open. The -6 diagnostic code is not active when the wire jumper is connected to the −Battery. Repair: There is a problem with the ECM. Perform the following procedure: 1. Temporarily connect a test ECM. Refer to Troubleshooting, "ECM - Replace" 2. Recheck the circuit to ensure that the original problem has been resolved. If the problem is resolved with the test ECM, install the suspect ECM. Before you consider replacing the ECM, consult the Dealer Solutions Network (DSN) for assistance. If the problem is not resolved with the test ECM, install the original ECM. There is a problem in the wiring.
7. Check the Voltage at the Connector for the Fuel Priming Pump A. Turn the battery disconnect switch to ON. B. Select diagnostic tests from Cat ET. C. Select the "Override Parameters" screen on Cat ET. D. Activate the override for the fuel pump relay. E. Measure the voltage between terminal 1 and terminal 2 at the connector for the fuel priming pump. Refer to Illustration 3 for the schematic of the circuit. F. Deactivate the override for the fuel pump relay. G. Turn the battery disconnect switch to OFF.	24 ± 3 VDC	Results: The voltage is 24 ± 3 VDC. Repair: The circuit for the fuel priming pump is operating correctly to the connector for the fuel priming pump. Verify that the fuel priming pump is operating correctly by testing the fuel priming pump. If a problem with the pump is discovered, replace the pump. Results: The voltage is not 24 ± 3 VDC. Verify that the return circuit at terminal 2 has continuity to the −Battery. If the return circuit is OK. Proceed to Test Step 8
8. Check for Power at the Connector for the Fuel Pump Relay A. Disconnect the fuel pump relay from the connector at the control box. B. Fabricate two jumper wires that are long enough to create a test circuit at the relay connector. Crimp spade terminals to one end of each of the jumper wires. C. Turn the battery disconnect switch to ON. D. Use the jumper wires and a multimeter to measure the voltage between terminal 1 and terminal 5 at the connector for the relay. The correct voltage measurement is 24 ± 3 VDC. E. Select the "Override Parameters" screen on Cat ET. F. Activate the override for the fuel pump relay. G. Use the jumper wires and a multimeter to measure the voltage between terminal 2 and terminal 5 at the connector for the relay. The correct voltage measurement is 24 ± 3 VDC. H. Deactivate the override for the fuel pump relay. I. Turn the battery disconnect switch to OFF. Restore the wiring to the original configuration.	24 ± 3 VDC	Results: The voltage is 24 ± 3 VDC. Repair: Replace the relay. Check if replacement of the relay has corrected the original problem. If the problem has not been resolved, there is a problem in the harness wiring between the relay and the fuel priming pump. The problem may be in the crossover harness that is in the control box. Repair the harness or replace the harness. Verify that the repair has resolved the original problem. Results: The voltage is not 24 ± 3 VDC for at least one of the measurements. Repair: If voltage is not present at either of the terminals, there is probably a problem in the circuit for the digital return at terminal 5. Check the continuity through the crossover harness from terminal 5 at the relay connector to terminal P2-14 at the ECM connector. If the voltage is incorrect at terminal 1 of the relay connector, check the +Battery circuit used to power the secondary circuit of the relay. Recheck the condition of the breaker that is for the manual override control at the low current power distribution panel. If the fuse is in good repair, check the voltage at terminal 3 of the connector for the high current power distribution panel. Repair the harness. Verify that the original problem has been resolved. If the voltage is incorrect at terminal 2 of the connector, there is a problem in the driver circuit from the ECM. There may be a problem with the ECM. Proceed to Test Step 9
9. Check for Proper Operation of the ECM A. Fabricate a jumper wire that is long enough to create a test circuit across the P1 ECM connector. Crimp a connector socket to one end of the jumper wire. B. At the J1/P1 ECM connector, use a wire removal tool to remove the wire from terminal location P1-10 (fuel pump relay). Insert the jumper wire into this terminal location. Note:Ensure that the loose end of the wire does not contact any ground source. C. Install a 7X-1709 Multimeter Probe (BLACK) onto the test lead of a multimeter. Note:Ensure that the multimeter probe is in good repair. A bent probe may contact other terminals inside the connector. D. Carefully insert the multimeter probe into terminal location P2-14 (digital return) at the ECM connector. E. Turn the battery disconnect switch to ON. F. Select the "Override Parameters" screen on Cat ET. G. Activate the override for the fuel pump relay. H. Use a multimeter to measure the voltage between the jumper wire and the multimeter probe while the override is active. Note:The correct voltage measurement is 24 ± 3 VDC. I. Turn the battery disconnect switch to OFF. J. Restore the wiring to the original configuration.	24 ± 3 VDC	Results: The voltage for the measurement is 24 ± 3 VDC. Repair: The output driver and the digital return at the ECM are OK. There is a problem in the crossover harness between the ECM and the relay connector. Locate the problem and repair the problem. Replace parts, if necessary. Verify that the original problem has been corrected. Results: The voltage for the measurement is not 24 ± 3 VDC. Repair: The problem is in one of the internal circuits for the ECM. Perform the following repair: 1. Temporarily connect a test ECM. Refer to Troubleshooting, "ECM - Replace" 2. Recheck the circuit to ensure that the original problem has been resolved. If the problem is resolved with the test ECM, install the suspect ECM. Before you consider replacing the ECM, consult with the Dealer Solutions Network (DSN) If the problem is not resolved with the test ECM, install the original ECM. There is a problem in the wiring.

If the procedure did not correct the issue, contact your Cat dealer Technical Communicator (TC). For further assistance, your TC can confer with the Dealer Solutions Network (DSN).