C3.3B and C3.8 Engines for Caterpillar Built Machines Caterpillar

DEF Pressure Is Low

Usage:

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表 1
Diagnostic Trouble Codes for DEF Pressure Is Low
J1939 Code and Description	Pre-Conditions for Code	Comments
4334-3 Aftertreatment #1 DEF #1 Pressure (absolute) : Voltage Above Normal	- Battery voltage is normal - Key switch signal (ECM: V13 & V33, DCU: 18 terminal) is continuously activated more than 2 sec - Starter Switch signal (ECM: V12 terminal) is not activated except within 2 sec after starter stopped - CAN communication is normal between DCU and engine ECM	Voltage of DEF pump pressure sensor is 4.7 V or more for 30 seconds or more.
4334-4 Aftertreatment #1 DEF #1 Pressure (absolute) : Voltage Below Normal		Voltage of DEF pump pressure sensor is 0.1 V or less for 30 seconds or more.
4334-15 Aftertreatment #1 DEF #1 Pressure (absolute) : High - least severe (1)	- Key switch signal (ECM: V13 & V33, DCU: 18 terminal) is not activated - Cooling down and Purge processes are completed - No DTC invalidation flag	DEF pressure is higher than the trigger value after purge process is completed (DEF pressure should be around 0 kPa in normal) 3 Ignition Cycles or more
4334-16 Aftertreatment #1 DEF #1 Pressure (absolute) : High - moderate severity (2)	- Key switch signal (ECM: V13 & V33, DCU: 18 terminal) is activated - Purge process is not completed - Thawing process is completed - DEF Pump is operating - DEF pressure target is not under-changing - DEF pump pressure sensor operation is normal - No DTC invalidation flag	Measured DEF pressure minus Target DEF pressure is higher than 100 kPa for at least 60 seconds. Stop DEF Injection.
4334-17 Aftertreatment #1 DEF #1 Pressure (absolute) : Low - least severe (1)	- Key switch signal (ECM: V13 & V33, DCU: 18 terminal) is not activated - Cooling down and Purge processes are completed - No DTC invalidation flag	DEF pressure is lower than the trigger value after purge process is completed (DEF pressure should be around 0 kPa in normal) 3 Ignition Cycles or more
4334-18 Aftertreatment #1 DEF #1 Pressure (absolute) : Low - moderate severity (2)	- Key switch signal (ECM: V13 & V33, DCU: 18 terminal) is activated - Purge process is not completed - Thawing process is completed - DEF Pump is operating - DEF pressure target is not under-changing - DEF pump pressure sensor operation is normal - No DTC invalidation flag	Measured DEF pressure minus Target DEF pressure is higher than 100 kPa for at least 60 seconds. Stop DEF Injection.
Follow the troubleshooting procedure to identify the root cause of the fault.

Two different troubleshooting procedures are required to cover the codes. The first troubleshooting table is for 4334-4, 4334-3, 4334-17, and 4334-15. The second troubleshooting step is for 4334-16 and 4334-18.

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图 1	g06148187

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表 2
Troubleshooting Test Steps	Values	Results
4334-4, 4334-3, 4334-17, and 4334-15
1. Check the DEF Pressure A. Turn the keyswitch to the ON engine not running.	Approximately 0 kPa	Result: DEF Pressure is not within specification. Repair: Replace DCU. Result: DEF Pressure is within specification. Proceed to Test Step 2.
2. Check the Voltage between DCU terminals 56 and 44 A. Turn key switch to OFF position. B. Disconnect DCU connector. C. Turn key switch to ON and measure the voltage between DCU terminals 56 and 44	Approximately 0.5V	Result: Voltage not within specification. Repair: Replace DCU. (no harness as root cause, sensor supply voltage?) Result: Voltage within specification. Proceed to Test Step 3.
3. Check the Voltage between DCU terminals 36 and 44 A. Turn key switch to ON and measure the voltage between DCU terminals 36 and 44.	Approximately 5.0	Result: Voltage not within specification. Repair: Replace DCU. Result: Voltage is within specification. Proceed to Test Step 4.
4. Check the Voltage on the DEF Pump A. Reconnect the DCU connector. B. Disconnect the DEF Pump connector. C. Turn the key switch to ON position and measure the voltage between the DEF Pump Terminals B and K on the wiring harness.	Approximately 0.5V	Result: Voltage not within specification, then check the harness between the DCU and the DEF Pump. Result: Voltage is within specification. Proceed to Test Step 5.
5. Measure the Voltage Between the DEF Pump A. Turn the key switch to the ON position and measure the voltage between the DEF pump unit connector at the wring harness side between terminals pin C and K.	Approximately 5.0	Result: Voltage not within specification, check the harness between the DCU and the DEF Pump. Result: Voltage is within specification. Repair: Replace the DEF pump.
6. Check DEF for diesel and DEF filter for swelling.Refer to Special Instructions, M0097723. ____________________

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表 3
Troubleshooting Test Steps	Values	Results
4334-16, 4334-18
1. Check the DEF lines A. Visually check that the DEF lines are not clogged, leaking, or broken.	Damaged or Clogged	Result: DEF lines are damaged or clogged. Repair: - Replace and clean parts as needed. - Clean the DEF Tank. Refer to Testing and Adjusting, "Diesel Exhaust Fluid Tank – Flush". - Check the DEF Quality. Refer to Testing and Adjusting, "Diesel Exhaust Fluid Quality – Test". Result: DEF lines are not damaged nor clogged. Proceed to Test Step 2.
2. Check that the DEF Tank Filter Is Not Clogged A. Check that the DEF Tank filter is not clogged. Refer to OMM, "DEF Tank –Disassembly and Assembly".	Clogged	Result: Filter is clogged. Repair: Replace the filter. Result: Filter is not clogged. Proceed to Test Step 3
3 Check that the DEF Pump Filter A. Check that the DEF Pump filter is not clogged. Refer to OMM, "DEF Pump Filter – Replace".	Clogged	Result: Filter is clogged. Repair: Replace the filter. Result: Filter is not clogged. Proceed to Test Step 4
4. Perform DEF Pump Circulation Test	Circulates	Result: The diagnostic code becomes active again. Repair: Replace the pump if this is for 5435-12. If this is for code 5435-1. Result: The diagnostic code does not become active.