C175 Tier 4 Final Engines for Off-Highway Trucks Caterpillar


DEF Pressure Does Not Respond

Usage:

793F D3T
Use this procedure to troubleshoot the Diesel Exhaust Fluid (DEF) pressure not responding. Also, use this procedure if one of the following event codes is active or logged.

Table 1
J1939 Code and Description  CDL Code and Description  Comments 
4334–7
Aftertreatment #1 DEF #1 Pressure (absolute) : Not Responding Properly 
3090–7
Aftertreatment #1 DEF Pressure Sensor : Not Responding Properly 
The Aftertreatment #1 Diesel Exhaust Fluid Control Unit (DCU) #1 detects signal voltage that is not in the acceptable range.
The code is logged. 
4387–7
Aftertreatment #2 DEF #1 Pressure (absolute) : Not Responding Properly 
3091–7
Aftertreatment #2 DEF #1 Pressure (absolute) : Not Responding Properly 
The Aftertreatment #2 DCU #1 detects signal voltage that is not in the acceptable range.
The code is logged. 
7459–7
Aftertreatment #1 DEF Doser #2 Absolute Pressure : Not Responding Properly 
5006–7
Aftertreatment #1 Diesel Exhaust Fluid Pressure #2 Sensor : Not Responding 
The Aftertreatment #1 DCU #2 detects signal voltage that is not in the acceptable range.
The code is logged. 
7464–7
Aftertreatment #2 DEF Doser #2 Absolute Pressure : Not Responding Properly 
5007–7
Aftertreatment #2 DEF Doser #2 Absolute Pressure : Not Responding Properly 
The Aftertreatment #2 DCU #2 detects signal voltage that is not in the acceptable range.
The code is logged. 

Table 2
Required Tools  Qty 
441-0451  Tool Gp 

Probable Causes

  • Codes

  • DEF lines

  • Pump filters

  • Header filters

  • DEF injector

  • Backflow valve

Recommended Actions

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

Table 3
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.
 


Illustration 1g06064951
The DEF pumps are on the front side of the Pump Electronic Tank Unit (PETU).
(1) Aftertreatment #1 DEF pump 1
(2) Aftertreatment #1 DEF pump 2
(3) Aftertreatment #2 DEF pump 1
(4) Aftertreatment #2 DEF pump 2


Illustration 2g06097979
The DEF injectors are on the inlet of the Clean Emissions Module (CEM). There are injectors on both inlets of the dual CEM applications.
(3) DEF injector 2 (Aftertreatment 1 DEF pump 1)
(4) DEF injector 3 (Aftertreatment 1 DEF pump 1)
(5) DEF injector 1 (Aftertreatment 1 DEF pump 2)
(6) DEF injector 4 (Aftertreatment 1 DEF pump 2)
(7) DEF injector 2 (Aftertreatment 2 DEF pump 1)
(8) DEF injector 3 (Aftertreatment 2 DEF pump 1)
(9) DEF injector 1 (Aftertreatment 2 DEF pump 2)
(10) DEF injector 4 (Aftertreatment 2 DEF pump 2)

Table 4
Troubleshooting Test Steps  Values  Results 

2. Inspect all 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"

Refer to Troubleshooting, Cat ET Service Features for additional information.

E. Visually inspect all DEF lines from the tank to the DEF injectors. Look for pinched, damaged, or disconnected lines.

F. Turn the keyswitch to OFF.
 

DEF Lines
 

Result: The lines are not leaking, damaged, pinched, or disconnected.

Proceed to Test Step 3.

Repair: The lines are leaking, damaged, pinched, or disconnected.

Result: Repair or replace the damaged components.

If the problem is not resolved, proceed to Test Step 3.
 

3. Verify that the DEF Lines Installed Correctly

A. Check each of the following locations:

- DEF pump
- DEF header
- Backflow valve
- DEF injectors

B. Check for excessive bending, pinching, or restrictions in the DEF lines.
 

Connections
 

Result: The DEF lines are routed to the correct locations.

Proceed to Test Step 4.

Repair: The DEF lines are not to the correct locations.

Result: Route the DEF lines to the correct locations.

Proceed to Test Step 10.
 


Illustration 3g06097983
(11) DEF suction line filter fitting
(12) DEF pump
(13) DEF pump filter cap

Table 5
Troubleshooting Test Steps  Values  Results 

4. Replace the DEF Pump Filters

A. Turn the keyswitch to OFF. Allow 2 minutes to elapse before proceeding.

B. Clean the area around the DEF pump filters.

C. Disconnect the suction line from the appropriate DEF pump.

D. Replace the DEF pump suction line filter fitting and DEF pump filter on the appropriate DEF pump. Refer to the Disassembly and Assembly manual for the additional information.
 

DEF Pump Filters
 

Result: The DEF pump filters were replaced.

Proceed to Test Step 5.
 

5. 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 6.
 


Illustration 4g06097984
(14) DEF header
(15) Sock filter
(16) DEF header filter

Table 6
Troubleshooting Test Steps  Values  Results 

6. Replace the Filters on the DEF Tank Header

A. Clean the area around the appropriate DEF header to prevent debris from contaminating the DEF tank.

B. Remove the appropriate DEF tank header from the DEF tank.

C. Replace the DEF tank header suction screen and sock filter.
 

Header Filters
 

Result: The DEF tank header filters were replaced.

Proceed to Test Step 7.
 

7. 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 8.
 

8. Check the DEF Injector for Leakage

A. Remove each of the DEF injector from the appropriate pump from the Clean Emissions Module (CEM). Refer to the Disassembly and Assembly manual for additional information. Place the injector into the container from the 441-0451 Tool Gp.

B. Turn the keyswitch to "ON". Do not start the engine.

C. Connect Cat ET.

D. Select the appropriate "DCU".

E. Perform the following diagnostic test:

- 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"

Refer to Troubleshooting, Cat ET Service Features for additional information.

F. With the DEF injectors removed, check for DEF flow from the affected injectors.

G. Turn the keyswitch to OFF.
 

Leakage 

Result: DEF did not leak from the injectors.

Proceed to Test Step 9.

Result: DEF leaked from one or both of the injectors.

Repair: Replace the failed DEF injector or injectors.

Proceed to Test Step 10.
 


Illustration 5g06097900
(17) DEF backflow valve for Aftertreatment 1 DEF pump 1 system
(18) DEF backflow valve for Aftertreatment 1 DEF pump 2 system
(19) DEF backflow valve for Aftertreatment 2 DEF pump 1 system
(20) DEF backflow valve for Aftertreatment 2 DEF pump 2 system

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 DEF backflow line from the DEF header assembly. Leave the DEF backflow line from the appropriate DEF pump to the back flow valve connected.

C. Run the DEF line from the back flow valve to the DEF header into the container in the 441-0451 Tool Gp. Remove the appropriate backflow valve from the PETU assembly if necessary.

D. Turn the keyswitch to ON. Do not start the engine.

E. Connect Cat ET.

F. Select the appropriate "DCU".

G. Perform the following diagnostic test:

- 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"

Refer to Troubleshooting, Cat ET Service Features for additional information.

H. While the test is running, verify that the DEF is flowing into the container.

Note: The test can be Canceled once DEF flow has been confirmed.
 

DEF Flow
 

Result: DEF did not flow from the backflow valve into the container.

Repair: A failed backflow valve has been detected. Replace the failed backflow valve.

Proceed to Test Step 10.

Result: DEF flowed from the backflow valve into the container.

Repair: A failed DEF pump has been detected. Replace the failed DEF pump.

Proceed to Test Step 10.
 

10. 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).

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