HUB 1066530 - Caterpillar

Table 1
Diagnostic Trouble Codes for DEF Pressure Is High
J1939 Code Description Notes
4334-0 Aftertreatment 1 Diesel Exhaust Fluid Doser Absolute Pressure : High - most severe (3) The ECM detects that the DEF pressure is greater than 750 kPa (109 psi) for at least 0.5 seconds.
The battery voltage is at least 10 V.
The warning lamp will flash and the engine will be derated. DEF injection is disabled when this diagnostic code is active.
The diagnostic code will clear when the DEF pressure drops below 750 kPa (109 psi) for at least 0.5 seconds.
4334-16 Aftertreatment 1 Diesel Exhaust Fluid Doser Absolute Pressure : High - moderate severity (2) The ECM detects that the DEF pressure has risen above 610 kPa (88 psi) and remains above 590 kPa (86 psi) for at least 20 seconds.
The battery voltage is at least 10 V.
The warning lamp will flash and the engine will be derated. When this diagnostic code becomes active, the DEF pressure will be reduced and the pressure build-up process will begin again .
The diagnostic code will clear if the DEF pressure remains below 610 kPa (88 psi) after the DEF system has been repressurized.
4374-18 Aftertreatment #1 Diesel Exhaust Fluid Pump Motor Speed : Low - moderate severity (2) The ECM detects that the PWM duty cycle for the DEF pump speed is less than 4 percent.
The battery voltage is at least 10 V.
The warning lamp will come on.
4375-18 Aftertreatment #1 DEF Pump Drive Command : Low - moderate severity (2) The ECM detects that the PWM duty cycle for the DEF pump control is less than 4 percent.
The battery voltage is at least 10 V.
The warning lamp will come on.
Follow the troubleshooting procedure to identify the root cause of the fault. Complete the procedure in the order in which the steps are listed.
Illustration 1 g03712848
View of the DEF pump module.
(1) DEF backflow line connector
Illustration 2 g03712856
View of the DEF tank and DEF tank header unit
(1) DEF backflow line connector
Table 2
Troubleshooting Test Steps Values Results
1. Check the Backflow Line for a Restriction
A. Turn the keyswitch to the OFF position for 2 minutes.
B. Remove the backflow line from DEF tank header (2) and DEF pump (1).
C. Inspect the backflow line for obstructions.
Note: Possible obstructions are ice, DEF deposits, or debris.
DEF return line restriction
Result: An obstruction was found.
Repair: Flush line with water/low pressure air. If necessary, replace the line.
Proceed to Test Step 3.
Result: An obstruction was not found.
Proceed to Test Step 2.
2. Check for Leaks in the Pressure Line and for Restriction in the DEF Pump
A. Connect the backflow line to DEF pump (2). Place the other end of the line into a suitable container to collect the DEF.
B. Remove the DEF injector from the SCR canister. Leave the coolant and DEF lines connected to the injector.
C. Turn the keyswitch to the ON position. Do not start the engine.
D. Connect to the electronic service tool.
E. Perform the "DEF Dosing System Verification Test". Wait for the test to complete.
F. Visually inspect the DEF pressure line and the DEF