C175 Tier 4 Final Engines for Off-Highway Trucks Caterpillar

Use this procedure to troubleshoot high Diesel Exhaust Fluid (DEF) pressure. 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
4334-15 Aftertreatment #1 DEF #1 Pressure (absolute) : High - least severe (1)	3090-20 Aftertreatment #1 DEF Pressure Sensor : Data Drifted High	The Diesel Exhaust Fluid Control Unit (DCU) detects that the Aftertreatment 1 Diesel Exhaust Fluid (DEF) pump 1 pressure is above the acceptable range. The code is logged.
4334-16 Aftertreatment #1 DEF #1 Pressure (absolute) : High - moderate severity (2)	E930 (1) High Aftertreatment #1 DEF Pressure	The DCU detects that the Aftertreatment 1 DEF pump 1 pressure is above the acceptable range. The code is logged.
4387-15 Aftertreatment #2 DEF #1 Pressure (absolute) : High - least severe (1)	3091-20 Aftertreatment #2 DEF #1 Pressure (absolute) : High - least severe (1)	The DCU detects that the Aftertreatment 2 DEF pump 1 pressure is above the acceptable range. The code is logged.
4387-16 Aftertreatment #2 DEF #1 Pressure (absolute) : High - moderate severity (2)	E932 (1) Aftertreatment #2 DEF #1 Pressure (absolute) : High - moderate severity (2)	The DCU detects that the Aftertreatment 2 DEF pump 1 pressure is above the acceptable range. The code is logged.
7459-15 Aftertreatment #1 DEF Doser #2 Absolute Pressure : High - least severe (1)	5006-20 Aftertreatment #1 Diesel Exhaust Fluid Pressure #2 Sensor : Data Drifted High	The DCU detects that the Aftertreatment 1 DEF pump 2 pressure is above the acceptable range. The code is logged.
7459-16 Aftertreatment #1 DEF Doser #2 Absolute Pressure : High - moderate severity (2)	E1705 (1) High Aftertreatment #1 DEF Pressure #2	The DCU detects that the Aftertreatment 1 DEF pump 2 pressure is above the acceptable range. The code is logged.
7464-15 Aftertreatment #1 DEF Doser #2 Absolute Pressure : High - least severe (1)	5007-20 Aftertreatment #1 Diesel Exhaust Fluid Pressure #2 Sensor : Data Drifted High	The DCU detects that the Aftertreatment 2 DEF pump 2 pressure is above the acceptable range. The code is logged.
7464-16 Aftertreatment #1 DEF Doser #2 Absolute Pressure : High - moderate severity (2)	E1707 (1) High Aftertreatment #1 DEF Pressure #2	The DCU detects that the Aftertreatment 2 DEF pump 2 pressure is above the acceptable range. The code is logged.

Probable Causes

• Codes

• Backflow line

• DEF pump

• Backflow valve

Recommended Actions

Illustration 1	g06100050
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 (5) Coolant diverter valve for Aftertreatment #1 DEF Pump #1 (6) Coolant diverter valve for Aftertreatment #1 DEF Pump #2 (7) Coolant diverter valve for Aftertreatment #2 DEF Pump #1 (8) Coolant diverter valve for Aftertreatment #2 DEF Pump #2 (9) Aftertreatment #1 DEF Pump #1 header (10) Aftertreatment #1 DEF Pump #2 header (11) Aftertreatment #2 DEF Pump #1 header (12) Aftertreatment #2 DEF Pump #2 header (13) Aftertreatment #1 DEF Pump #1 backflow valve (14) Aftertreatment #1 DEF Pump #2 backflow valve (15) Aftertreatment #2 DEF Pump #1 backflow valve (16) Aftertreatment #2 DEF Pump #2 backflow valve (17) Aftertreatment #1 DEF Pump #1 electrical connection for DEF header (18) Aftertreatment #1 DEF Pump #2 electrical connection for DEF header (19) Aftertreatment #2 DEF Pump #1 electrical connection for DEF header (20) Aftertreatment #2 DEF Pump #2 electrical connection for DEF header

Table 2

Troubleshooting Test Steps	Values	Results
1. Check the 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 any associated codes before continuing with this test. Result: A code is active or logged. Proceed to Test Step 2.
2. Check the Backflow Lines for a Restriction A. Turn the keyswitch to the OFF position. Allow 2 minutes to elapse before proceeding. B. Remove the appropriate backflow line between the backflow valve and the Diesel Exhaust Fluid (DEF) tank header. C. Inspect the backflow lines for obstructions. Flush line with water/low pressure air if necessary. Possible obstructions are ice, DEF deposits, or debris.	Restriction	Result: An obstruction was found in the backflow line. Repair: Flush the line or replace the line. Proceed to Test Step 5. Result: An obstruction was not found in the backflow line. Proceed to Test Step 3.

Illustration 2	g06026979

Table 3

3. Check for a Restriction in the DEF Pump A. Reinstall the backflow line onto the DEF pump. Place the end of the line that would normally be installed onto the backflow valve into a beaker to collect the DEF. B. Turn the keyswitch to the ON position. Do not start the engine. C. Connect Cat ET. D. Select the "Catalyst Reduction System". E. Use Cat ET to 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 CANCEL to abort the test.	DEF	Result: DEF flowed from the backflow line into the container. Reinstall the backflow line onto the backflow valve. Proceed to Test Step 4. Result: DEF did not flow from the DEF backflow line into the container. Repair: Replace the DEF pump and reinstall all DEF lines. Refer to the Disassembly and Assembly manual for the additional information. Proceed to Test Step 5.
4. Check for a Failed Backflow Valve A. Reinstall the backflow line onto the backflow valve. Place the end of the line that would normally be installed onto the DEF header into a beaker to collect the DEF. B. Turn the keyswitch to the ON position. Do not start the engine. C. Connect Cat ET. D. Select the "Catalyst Reduction System". E. Use Cat ET to 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 CANCEL to abort the test.	DEF	Result: DEF flowed from the backflow line into the container. Reinstall the backflow line onto the DEF header. Proceed to Test Step 5. Result: DEF did not flow from the DEF backflow line into the container. Repair: Replace the backflow valve and reinstall all DEF lines. Refer to the Disassembly and Assembly manual for the additional information. Proceed to Test Step 5.
5. Perform an "Aftertreatment Dosing System Functional Test" A. Turn the keyswitch to the ON position. Do not start the engine. B. Connect Cat ET. C. Select the "Selective Catalyst Reduction System". D. Use Cat ET to 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).