C175 Tier 4 Final Engines for Off-Highway Trucks Caterpillar

DEF Pressure Is Low

Usage:

793F D3T

Use this procedure to troubleshoot low Diesel Exhaust Fluid (DEF) pressure. Also, use this procedure if one of the following event codes is active or logged.

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Table 1
J1939 Code and Description	CDL Code and Description	Comments
4334-17 Aftertreatment #1 DEF #1 Pressure (absolute) : Low - least severe (1)	E931 (1) Low Aftertreatment #1 DEF Pressure #1	The Diesel Exhaust Fluid (DEF) system pressure dropped below the acceptable threshold during dosing on aftertreatment #1 pump #1.
4387-17 Aftertreatment #2 DEF #1 Pressure (absolute) : Low - moderate severity (2)	E933 (1) Aftertreatment #2 DEF #1 Pressure (absolute) : Low - moderate severity (2)	The DEF system pressure dropped below the acceptable threshold during dosing on aftertreatment #2 pump #1.
5392-31 Aftertreatment #1 DEF Dosing Unit #1 Loss of Prime	E1370 (1) Aftertreatment #1 DEF Dosing Unit #1 Loss of Prime	The DEF system pressure was not achieved during priming on aftertreatment #1 pump #1.
5748-31 Aftertreatment #2 DEF Dosing Unit #1 Loss of Prime	E1371 (1) Aftertreatment #2 DEF Dosing Unit #1 Loss of Prime	The DEF system pressure was not achieved during priming on aftertreatment #2 pump #1
7459-17 Aftertreatment #1 DEF Doser #2 Absolute Pressure : Low - least severe (1)	E1706 (1) Low Aftertreatment #1 DEF Pressure #2	The DEF system pressure dropped below the acceptable threshold during dosing on aftertreatment #1 pump #2.
7464-17 Aftertreatment #2 DEF Doser #2 Absolute Pressure : Low - least severe (1)	E1708 (1) Low Aftertreatment #2 DEF Pressure #2	The DEF system pressure dropped below the acceptable threshold during dosing on aftertreatment #2 pump #2.
7541-31 Aftertreatment #1 DEF Dosing Unit #2 Loss of Prime	E1666 (1) Aftertreatment #1 DEF Dosing Unit #2 Loss of Prime	The DEF system pressure was not achieved during priming on aftertreatment #1 pump #2.
7542-31 Aftertreatment #2 DEF Dosing Unit #2 Loss of Prime	E1667 (1) Aftertreatment #2 DEF Dosing Unit #2 Loss of Prime	The DEF system pressure was not achieved during priming on aftertreatment #2 pump #2.

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Table 2
Associated Codes
J1939 Code	CDL Code	Troubleshooting Procedure
1761-1	E954 (3)	Troubleshooting, "DEF Tank Level Is Low"
1761-17	E954 (1)	Troubleshooting, "DEF Tank Level Is Low"
1761-18	E954 (2)	Troubleshooting, "DEF Tank Level Is Low"
7598-5	5024-5	Troubleshooting, "Solenoid Valve - Test (Aftertreatment)"
7598-6	5024-6	Troubleshooting, "Solenoid Valve - Test (Aftertreatment)"
7599-5	5025-5	Troubleshooting, "Solenoid Valve - Test (Aftertreatment)"
7599-6	5025-6	Troubleshooting, "Solenoid Valve - Test (Aftertreatment)"
7600-5	5026-5	Troubleshooting, "Solenoid Valve - Test (Aftertreatment)"
7600-6	5026-6	Troubleshooting, "Solenoid Valve - Test (Aftertreatment)"
7601-5	5027-5	Troubleshooting, "Solenoid Valve - Test (Aftertreatment)"
7601-6	5027-6	Troubleshooting, "Solenoid Valve - Test (Aftertreatment)"

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Table 3
Required Tools		Qty
441-0451	Tool Gp	1

Probable Causes

Codes
DEF filters
Connectors and Wiring
Leaks
DEF quality
DEF lines
Voltage
DEF pump
Backflow valve

Recommended Actions

Reference: Refer to Troubleshooting, System Overview (Aftertreatment Identification) for locating aftertreatment components if necessary.

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Table 4
Troubleshooting Test Steps	Values	Results
1. Check for Codes A. Connect Cat^® Electronic Technician (ET) to the service tool connector. B. Look for active codes that are associated with the system for the event code.	Codes	Result: An associated code is active. Repair: Troubleshoot the associated code before continuing with this test. Result: A code is active or logged. Proceed to Test Step 2.
2. Inspect the DEF Tank Vent Line, Breather, and Fill Cap for Debris	Debris	Results: The vent line, breather, and DEF tank fill showed no signs of debris accumulation. Proceed to Test Step 3. Results: The components show signs of debris accumulation. Repair: Remove and clean the contaminated components with warm water. Reinstall the components. Proceed to Test Step 3.
3. Inspect the Electrical Connectors and the Wiring A. Turn the keyswitch to OFF. B. Inspect the electrical connections to each DEF tank header. Refer to Troubleshooting, "Electrical Connectors - Inspect" for additional information. C. Inspect the connections for corrosion or loose wires.	Connectors and Wiring	Result: The connectors and wiring appear to be OK. Proceed to Test Step 4. Result: There is a problem with the connectors and/or wiring. Repair: Repair or replace the connectors or wiring. Ensure that all the seals are properly in place and ensure that the connectors are coupled. Proceed to Test Step 11.
4. Inspect the DEF Lines for Leaks A. Turn the keyswitch to ON. Do not start the engine. B. Connect Cat ET. C. Select the appropriate Diesel Exhaust Fluid Control Unit (DCU). D. Perform the following diagnostic test to pressurize the system: - For Aftertreatment #1 DEF System #1 perform the "Aftertreatment #1 DEF Dosing System #1 Prime Test" - For Aftertreatment #1 DEF System #2 perform the "Aftertreatment #1 DEF Dosing System #2 Prime Test" - For Aftertreatment #2 DEF System #1 perform the "Aftertreatment #2 DEF Dosing System #1 Prime Test" - For Aftertreatment #2 DEF System #2 perform the "Aftertreatment #2 DEF Dosing System #2 Prime Test" E. Inspect all DEF lines from the tank to the DEF injector. Check for pinched, damaged, disconnected, or leaking lines. F. Turn the keyswitch to "OFF".	DEF Lines	Result: A leaking or disconnected line was found. Repair: Repair or replace the failed DEF line. Proceed to Test Step 11. Result: A leaking or disconnected line was not found. Proceed to Test Step 5.
5. Check the DEF Quality A. Measure the DEF quality. Refer to Testing and Adjusting, Diesel Exhaust Fluid Quality - Test for additional information.	DEF	Result: The DEF is not contaminated. Proceed to Test Step 6. Result: The DEF is contaminated. Repair: Contact the Dealer Solutions Network (DSN) for further information.

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Illustration 1	g06238471
(1) Suction line for aftertreatment #1 pump #1 system (2) Suction line for aftertreatment #1 pump #2 system (3) Suction line for aftertreatment #2 pump #1 system (4) Suction line for aftertreatment #2 pump #2 system

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Table 5
Troubleshooting Test Steps	Values	Results
6. Check for Suction Line Restrictions A. Disconnect the suction line from the affected DEF tank header and affected DEF pump. B. Inspect the suction line for obstructions or damage. Also, check that the line is connected in the proper locations. Note: Possible obstructions are ice, DEF deposits, or debris.	Restrictions	Result: An obstruction or damage was found. Repair: Flush the line with water or low-pressure air or replace the suction line. Proceed to Test Step 11. Result: An obstruction or damage was not found. Reinstall the suction line. Proceed to Test Step 7.

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Illustration 2	g06238472
(5) DEF suction line filter fitting (6) DEF pump (7) DEF pump filter cap

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Table 6
Troubleshooting Test Steps	Values	Results
7. Replace the Affected DEF Pump Filters A. Clean the area around the affected pump filters. B. Replace the DEF pump suction line filter fitting and DEF pump filter on the affected DEF pump.	DEF Pump Filters	Result: The affected DEF pump filters were replaced. Proceed to Test Step 8.
8. Check the DEF Pump A. Turn the keyswitch to ON. Do not start the engine. B. Connect Cat ET. C. Select the appropriate DCU. D. Perform the following diagnostic test to pressurize the system: - For DEF System #1 perform the "Aftertreatment #1 DEF Dosing System #1 Prime Test" - For DEF System #2 perform the "Aftertreatment #1 DEF Dosing System #2 Prime Test" - For Aftertreatment #2 DEF System #1 perform the "Aftertreatment #2 DEF Dosing System #1 Prime Test" - For Aftertreatment #2 DEF System #2 perform the "Aftertreatment #2 DEF Dosing System #2 Prime Test" E. Use Cat ET to monitor the DEF Pressure during the test to see if the pressure stabilizes.	DEF Pump	Result: The DEF pump maintained at least 800 kPa (116 psi) during the test. Proceed to Test Step 10. Result: The DEF pump did not maintain at least 800 kPa (116 psi) during the test. Proceed to Test Step 9.

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Illustration 3	g06238480
(8) DEF backflow valve for aftertreatment #1 pump #1 system (9) DEF backflow valve for aftertreatment #1 pump #2 system (10) DEF backflow valve for aftertreatment #2 pump #1 system (11) DEF backflow valve for aftertreatment #2 pump #2 system

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Table 7
Troubleshooting Test Steps	Values	Results
9. Check the Backflow Valve A. Turn the keyswitch to OFF. Allow 2 minutes to elapse before proceeding. B. Disconnect the electrical and DEF line connections from the affected backflow valve. C. Remove the affected backflow valve from the pump electronics tank unit (PETU) assembly. D. Pour water or blow low-pressure air through the large fitting on the backflow valve. Do NOT pour water or blow air through the small fitting as this may lift the valve off the seat and cause the backflow valve to appear to be failed. Note: The backflow valve is normally closed and water/low-pressure air should not flow through the large fitting to the small fitting on the backflow valve assembly.	Backflow Valve	Result: The water/low-pressure air does not flow through the backflow valve. Repair: Replace the DEF pump. Refer to the Disassembly and Assembly manual for additional information. Proceed to Test Step 11. Result: The water/low-pressure air flows through the backflow valve. Repair: Replace the failed backflow valve. Refer to the Disassembly and Assembly manual for additional information. Proceed to Test Step 11.

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Illustration 4	g06238484
(12) DEF header (13) Sock filter (14) DEF header filter

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Table 8
Troubleshooting Test Steps	Values	Results
10. Replace the Filters and Flush the DEF Tank A. Turn the keyswitch to OFF. B. Remove the DEF header from the DEF tank. C. Flush the DEF tank. Refer to Testing and Adjusting, "Diesel Exhaust Fluid Tank - Flush" for additional information. D. Replace the DEF header filter and DEF header sock filter on each of the DEF headers. Refer to Testing and Adjusting, "Diesel Exhaust Fluid Tank - Flush" for additional information.	DEF Tank Filters	Result: The DEF tank was flushed and the filters were replaced. Proceed to Test Step 11.

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Illustration 5	g06026979

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Table 9
Troubleshooting Test Steps	Values	Results
11. Perform an "Aftertreatment Dosing System Functional Test" A. Turn the keyswitch to ON. Do not start the engine. B. Connect Cat ET. C. Select the "Selective Catalyst Reduction System". D. Perform the following diagnostic test: -"Aftertreatment Dosing System Functional Test" Refer to Troubleshooting, Cat ET Service Features for additional information. Note: When the test prompts to proceed to clear active diagnostics, select ACCEPT.	Test	Result : The test was successful. Return to service. Result : The test was not successful. Proceed to Test Step 12.
12. Perform the "DEF Dosing System Accuracy Test" A. Turn the keyswitch to OFF. Allow 2 minutes to elapse before proceeding. B. Remove each of the DEF injectors from the affected DEF pump. C. Connect Cat ET. D. Select the appropriate DCU. E. Use Cat ET to perform the following diagnostic test on the appropriate DEF injector: -"Aftertreatment #X DEF Dosing Injector #X Accuracy Test" Refer to Testing and Adjusting, "DEF Dosing System Accuracy Test" for additional information.	Test	Result: The amount of DEF collected on one or more of the DEF injectors was less than 170 mL. A failed DEF injector has been detected. Repair: Replace the failed DEF injector(s). Proceed to Test Step 13. Result: The amount of DEF collected on one or more injectors was above 190 ml. A failed DEF injector has been detected. Repair: Replace the failed DEF injector(s). Proceed to Test Step 13.
13. Perform an Aftertreatment Dosing System Functional Test A. Turn the keyswitch to ON. Do not start the engine. B. Connect Cat ET. C. Select the "Selective Catalyst Reduction System". D. Perform the following diagnostic test: -"Aftertreatment Dosing System Functional Test" Refer to Troubleshooting, Cat ET Service Features for additional information. Note: When the test prompts to proceed to clear active diagnostics, select "ACCEPT".	Test	Result: The test was successful. 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).