C3.4B Engines DEF Pressure Is Low Caterpillar

DEF Pressure Is Low

C3.4B Engines [UENR4499]

C3.4B Engines DEF Pressure Does Not Respond

C3.4B Engines DEF Tank Level Is Low

AIR INLET AND EXHAUST SYSTEM

AFTERTREATMENT GP

C3.4B Engines DEF Concentration Is Incorrect

C3.4B Engines DEF Module Does Not Respond

C3.4B Engines DEF Pressure Is High

C3.4B Engines DEF Does Not Purge

C3.4B Engines DEF Pressure Does Not Respond

C3.4B Engines DEF Pressure Is Low

C3.4B Engines DEF Tank Level Is Low

This procedure covers the following diagnostic code:

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Table 1
Diagnostic Trouble Codes for DEF Pressure Is Low
J1939 Code	Description	Notes
4334-18	Aftertreatment 1 Diesel Exhaust Fluid Doser Absolute Pressure : Low - moderate severity (2)	The Electronic Control Module (ECM) detects that the Diesel Exhaust Fluid (DEF) pressure has dropped below 390 kPa (57 psi) and remains below 410 kPa (59 psi) for at least 40 seconds. The warning lamp will flash. The engine will be derated.
4374-15	Aftertreatment #1 Diesel Exhaust Fluid Pump Motor Speed : High - least severe (1)	The ECM detects that the duty cycle of the DEF pump required to maintain DEF pressure is too high. The DEF system is not dosing. The battery voltage is at least 10 V. The warning lamp will flash. The engine will be derated.
4375-16	Aftertreatment #1 DEF Pump Drive Command : High - moderate severity (2)	The ECM detects that the PWM duty cycle for the DEF pump control is greater than 86 percent. The battery voltage is at least 10 V. The warning lamp will come on.
Follow the troubleshooting procedure in order to identify the root cause of the problem.

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Illustration 1	g03713516
View of the DEF pump module (1) DEF backflow line connector (2) DEF pressure line connector (3) DEF suction line connector

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Illustration 2	g03713528
View of the DEF tank and DEF tank header unit (4) DEF backflow line connector (5) DEF suction line connector

Complete the procedure in the order in which the steps are listed.

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Table 2
Troubleshooting Test Steps	Values	Results
1. Check the DEF Gauge A. Turn the keyswitch to the ON position. B. Check the current position of the DEF gauge. C. Clean dirt and debris from around the tank filler cap before removing the cap. Add DEF to the DEF tank. D. Check for a change in the gauge position. E. If the gauge is in the full position, drain DEF from the tank and look for a change in the gauge position.	Gauge position	Result: The gauge did not move by adding or removing fluid to the tank. Repair: Remove the DEF tank header and check for a stuck float. If the float was not stuck, replace the DEF tank header. Return the unit to service. If the float was stuck, repair the stuck float using the DEF Manifold Sensor Kit. Refer to Disassembly and Assembly, Manifold (DEF Heater) Sensor - Disassemble (Temperature, Level, Quality DEF Manifold Sensor) and Manifold (DEF Heater) Sensor - Assemble (Temperature, Level, Quality DEF Manifold Sensor) Result: The gauge moved by adding or removing fluid to the tank. Proceed to Test Step 2.
2. Check the DEF Suction and Backflow Line Connections A. Check that the DEF suction and backflow lines are connected to the correct connectors. Refer to Illustration 1 and Illustration 2.	DEF line connections	Result: The DEF lines have been installed to the incorrect connectors. Repair: Connect the DEF lines to the correct connectors. Refer to Illustration 1 and Illustration 2. Result: The DEF lines are installed correctly. Proceed to Test Step 3.
3. Inspect the DEF Lines for Leaks A. Turn the keyswitch to the ON position. Do not start the engine. B. Connect to the electronic service tool. C. Perform the "DEF Dosing System Verification Test" to pressurize the system. Refer to Troubleshooting, "Service Tool Features" for more information. D. Inspect all of the DEF lines for disconnected lines or leaks.	Leaks	Result: A leaking or disconnected line was found. Repair: Repair or replace the faulty DEF line. Result: A leaking or disconnected line was not found. Proceed to Test Step 4.
4. Inspect the DEF Tank Filler Cap A. Clean dirt and debris from around the filler cap before removing the cap. Blockages can be caused by a build-up of dirt/debris around the filler cap. B. Remove the cap. C. Visually inspect the DEF tank filler cap for blockages.	Filler cap	Result: The cap has a blockage. Repair: Replace the cap. Result: A blockage was not found. Proceed to Test Step 5.
5. Check for Suction Line Restrictions A. Disconnect suction the line from DEF pump module (3) and DEF tank header (5). Refer to Illustration 1 and Illustration 2. B. Inspect the suction line for obstructions. Possible obstructions are ice, DEF deposits, or debris.	Restrictions	Result: An obstruction was found. Repair: Flush the line with water or low-pressure air or replace the suction line. Result: An obstruction was not found. Install the suction line. Proceed to Test Step 6.
6. Replace the Filters and Flush the DEF Tank A. Turn the keyswitch to the OFF position for 2 minutes. B. Flush the DEF tank. Refer to Systems Operation, Testing and Adjusting, "Diesel Exhaust Fluid Tank - Flush" for the correct procedure. C. Replace the DEF tank header filter and DEF pump filter. Refer to Systems Operation, Testing and Adjusting, "Diesel Exhaust Fluid Tank - Flush" for the correct procedure.	DEF filter	Result: The DEF tank was flushed and the filters were replaced. Proceed to Test Step 7.
7. Check for a Leaking DEF Injector A. Perform the DEF dosing system accuracy test. Refer to Systems Operation, Testing and Adjusting, "Aftertreatment SCR System Dosing Test" for the correct procedure.	DEF Dosing	Result: The quantity of DEF collected is not within the acceptable range. Repair: Replace the DEF injector. Refer to Disassembly and Assembly, "DEF Injector and Mounting - Remove and Install" Result: The quantity of DEF collected is within the expected range. Repair: Replace the DEF pump. Refer to Disassembly and Assembly, "Diesel Exhaust Fluid Pump - Remove and Install".