C175-20 Locomotive Engine Caterpillar

DEF Pressure Is Low

Usage:

Use this procedure to troubleshoot a problem with low Diesel Exhaust Fluid (DEF) pressure. Also, use this procedure if the following event code is active or logged.

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Table 1
J1939 Code and Description	CDL Code and Description	Comments
6875-18 Aftertreatment #1 DEF Dosing Pressure : Low - least severe (1)	E931 (1) Low Aftertreatment #1 DEF Pressure	The Diesel Exhaust Fluid (DEF) pressure is below the threshold for proper system operation. DEF dosing is disabled.

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Table 2
Associated Codes
J1939 Code	CDL Code	Troubleshooting Procedure
4335-15	E1969 (1)	Troubleshooting, "Air Assist Pressure Is High"
4335-17	E964 (1)	Troubleshooting, "Air Assist Pressure Is Low"
4335-18	E964 (2)	Troubleshooting, "Air Assist Pressure Is Low"
4335-3	3092-3	Troubleshooting, "Sensor Signal (Analog, Active) - Test"
4335-4	3094-4	Troubleshooting, "Sensor Signal (Analog, Active) - Test"
4376-5	3862-5	Troubleshooting, "Solenoid Valve - Test"
4376-6	3862-6	Troubleshooting, "Solenoid Valve - Test"
6875-3	3090-3	Troubleshooting, "Sensor Signal (Analog, Active) - Test"
6875-4	3090-4	Troubleshooting, "Sensor Signal (Analog, Active) - Test"
7107-5	N/A	Troubleshooting, "DEF Pump Motor - Test"
7107-6	N/A	Troubleshooting, "DEF Pump Motor - Test"
7107-11	N/A	Troubleshooting, "DEF Pump Motor - Test"
7416-5	N/A	Troubleshooting, "Solenoid Valve - Test - Aftertreatment"
7416-6	N/A	Troubleshooting, "Solenoid Valve - Test - Aftertreatment"
7417-2	N/A	Troubleshooting, "DEF Pump Power Supply - Test"
7417-5	N/A	Troubleshooting, "Circuit Breaker - Test"
7417-6	N/A	Troubleshooting, "Circuit Breaker - Test"

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Illustration 1	g03747254
Enhanced Troubleshooting Information (ETI) code

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Illustration 2	g06385290
DEF Component Locations (1) DEF Injector Nozzle (2) DEF Inlet Line Connection (3) DEF Pump (4) DEF Pressure Sensor

Probable Causes

Codes
Gas temperature
Sensor
Leaks
DEF line
Voltage
LED light
DEF pump
Debris

Recommended Actions

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Table 3
Troubleshooting Test Steps	Values	Results
1. Check for Codes A. Turn the DC breaker to the ON position. B. Connect Cat^® Electronic Technician (ET) to the service tool connector. C. Look for active codes that are associated with the system for the event code.	Codes	Result: An associated code is active. Repair: Troubleshoot any associated codes before continuing with this test. Result: A code is active or logged. Record the Enhanced Troubleshooting Information (ETI) code with the event. Refer to Illustration 1 for the ETI code location. Proceed to Test Step 2.
2. Monitor the Catalyst Intake Gas Temperature A. Turn the DC breaker to the ON position. B. Connect Cat ET. C. Use Cat ET to monitor the following temperature: - "Aftertreatment #1 SCR Catalyst Intake Gas Temperature"	Temperature	Result: The "Aftertreatment #1 SCR Catalyst Intake Gas Temperature" is less than 180° C (356° F) Proceed to Test Step 3. Result: The "Aftertreatment #1 SCR Catalyst Intake Gas Temperature" is 180° C (356° F) or higher. Repair: Use Cat ET to perform the following override: - Set the "Aftertreatment #1 SCR Dosing Air Assist Valve Command Override" to the OFF position. Proceed to Test Step 3.
3. Check the Diesel Exhaust Fluid (DEF) Pressure Sensor A. Turn the DC breaker to the ON position. B. Connect Cat ET. C. Use Cat ET to monitor the following pressure: - "Aftertreatment #1 DEF Dosing Pressure"	Sensor	Result: The DEF pressure sensor reads 0 ± 20 kPa (0 ± 3 psi). Proceed to Test Step 4. Result: The DEF pressure sensor does not read 0 ± 20 kPa (0 ± 3 psi). Repair: Replace the DEF pressure sensor. Proceed to Test Step 13.
4. Inspect for DEF and Air Leaks A. Turn the DC breaker to the OFF position. B. Inspect the DEF lines between the remote DEF supply and the dosing cabinet. C. Inspect the lines and manifold inside the dosing cabinet. D. Inspect the DEF lines between the dosing cabinet and the DEF injector. E. Inspect the air lines for signs of leakage and ensure that lines are connected.	DEF and Air Leaks	Result: There were no DEF or air leaks. Proceed to Test Step 5. Result: There were DEF and/or air leaks. Repair: Repair or replace damaged components. Proceed to Test Step 13.
5. Determine the ETI Code A. Use the ETI code recorded in Step 1 to determine the troubleshooting.	Code	Result: An ETI code of 1 is present. Proceed to Test Step 6. Result: An ETI code of 3 is present. Proceed to Test Step 7. Result: An ETI code of 4 is present. Repair: A failed DEF return valve has been detected. Replace the DEF return valve. Proceed to Test Step 13.
6. Inspect the DEF/Air Pressure Line A. Turn the DC breaker to the OFF position. B. Disconnect the DEF pressure line from the dosing cabinet. C. Disconnect the DEF pressure line from the DEF injector. D. Pour warm water through the DEF pressure line and verify that the line is not blocked.	DEF Line	Result: The DEF/Air pressure line is blocked. Repair: Clean the DEF/Air pressure line. Proceed to Test Step 13. Result: The DEF/Air pressure line is not blocked. Repair: A blocked DEF injector has been detected. Clean or replace the DEF injector. Proceed to Test Step 13.
7. Check for Power at the DEF Pump A. Turn the AC breaker, on the front face of the dosing cabinet, to the ON position. B. Measure the voltage supply to the DEF pump at the circuit breaker.	120 VAC	Result: There was 120 VAC at the circuit breaker. Proceed to Test Step 8. Result: There was not 120 VAC at the circuit breaker. Repair: There is a problem with the power supply to the dosing cabinet. For information on the power supply, refer to the Original Equipment Manufacturers (OEM) service information. If the problem is not resolved, proceed to Test Step 13.
8. Check the Wiring to the DEF Pump for an Open Circuit A. Turn the AC and DC breakers to the OFF position. B. Disconnect the J1 connector from the Selective Catalyst Reduction (SCR) controller. C. Disconnect the 5-pin connector from the DEF pump. D. Measure the resistance between the following pins: - Pin 38 SCR controller J1 connector and Pin 1 DEF pump 5-pin connector. - Pin 5 SCR controller J1 connector and Pin 4 DEF pump 5-pin connector.	Open Circuit	Result: There were more than 10 ohms of resistance between the following pins. Repair: An open circuit has been detected. Repair or replace the wiring harness. Proceed to Test Step 13. Result: There were less than 10 ohms of resistance between the following pins. Repair: The wiring harness is OK. Proceed to Test Step 9.
9. Check the LED Pump Status Light on the DEF Pump Screen A. Turn the AC breaker, on the front face of the dosing cabinet, to the ON position. B. Observe the LED light on the pump screen.	LED Light Status	Result: The LED pump status light is ON STEADY(not flashing). Proceed to Test Step 10. Result: The LED pump status light is FLASHING. Repair: Press the "PLAY" button on the pump screen, the LED status light should be ON STEADY. Proceed to Test Step 10.
10. Check the DEF Pump A. Turn the AC breaker, on the front face of the dosing cabinet, to the OFF position. Turn the DC breaker, located in the power distribution box, to the OFF position. B. Remove the DEF line that runs to the DEF injector from the dosing cabinet. C. Install the DEF line attachment included in the 464-1955 Tool Gp. D. Run the DEF line into the container included in the 464-1955 Tool Gp. E. Turn the AC breaker, on the front face of the dosing cabinet, to the ON position. Turn the DC breaker, located in the power distribution box, to the ON position. F. Connect CatET. G. Use Cat ET to perform the following test: -"DEF Dosing System Accuracy Test". Note: While performing this test, the test hose can contain up to an extra 140 mL (4.76 oz) of fluid.	2 L 200 ml	Result: The test returned 2.2 L (2.325 qt) of DEF. Proceed to Test Step 13. Result: The test did not return 2.2 L (2.325 qt) of DEF. Proceed to Test Step 11.
11. Check the Dosing Cabinet DEF Tank Suction Line Strainer for Blockage A. Remove the DEF tank header assembly from the DEF tank. B. Inspect the suction line strainer for a blockage or debris.	Blockage/Debris	Result: The suction line strainer was not blocked. Proceed to Test Step 12. Result: The suction line strainer was blocked. Repair: Clean the suction line strainer. Proceed to the Test Step 10 to retest the DEF pump output.
12. Inspect the Pump Check Valves for Blockage or Failure A. Turn the AC breaker, on the front face of the dosing cabinet, to the OFF position. Turn the DC breaker, located in the power distribution box, to the OFF position. B. Remove the manifold from the DEF pump. Refer to Disassembly and Assembly, Control Cabinet - Disassemble for additional information. C. Inspect the two check valves for blockage or failure.	Blockage or Failure	Result: Blockage or a failed check valve was found. Repair: Clean or replace the check valves. Proceed to Test Step 13. Result: No blockage or failure was observed. A failed DEF pump has been detected. Repair: Replace the DEF pump. Proceed to Test Step 13.
13. Operate the Engine A. Turn the AC breaker, on the front face of the dosing cabinet, to the OFF position for at least 1 minute. Turn the DC breaker, located in the power distribution box, to the OFF position for at least 1 minute. B. Turn the AC breaker, on the front face of the dosing cabinet, to the ON position. Turn the DC breaker, located in the power distribution box, to the ON position. C. Start the engine. D. Run the engine until normal operating temperature is reached. E. Connect Cat ET . F. Use Cat ET to monitor the following: - "Aftertreatment System State" G. Check for fault codes when the "Aftertreatment System State" reads "Normal Dosing".	Codes	Result: A code is not active. Return to service.

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).