TURBO GP-BASIC 0R5751 - Caterpillar

Table 1
Diagnostic Trouble Codes for DEF Does Not Purge
J1939 Code Description Notes
4334-20 Aftertreatment 1 Diesel Exhaust Fluid Doser Absolute Pressure : Data Drifted High The ECM detects that the DEF pressure is greater than the acceptable range by at least 35 kPa (5 psi) after the DEF system has purged. The acceptable range is determined by ambient conditions and DEF tank temperature.
The battery voltage is at least 10 V.
The warning lamp will come on.
This diagnostic code will clear the next time the keyswitch is turned to the ON position.
4334-21 Aftertreatment 1 Diesel Exhaust Fluid Doser Absolute Pressure : Data Drifted Low The ECM detects that the DEF pressure is less than the acceptable range by at least 75 kPa (11 psi) after the DEF system has purged. The acceptable range is determined by ambient conditions and DEF tank temperature.
The battery voltage is at least 10 V.
The warning lamp will come on.
This diagnostic code will clear the next time the keyswitch is turned to the ON position.
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
Required Tools
Tool Part Number Part Description Qty
A 481-9905 Test Kit (DEF) 1
B 503-9003 Container Assembly 1
Table 3
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 de-ionized water or low-pressure air. If necessary, replace the line.
Result: An obstruction was not found.
Proceed to Test Step 2.
2. Check That The Backflow Valve Opens During the Purge Cycle
A. Remove the backflow line from DEF pump connector (1).
B. Place the DEF injector into the container from Tooling (B).
C. Place a suitable container to collect the DEF from the backflow connector on the DEF pump.
D. Use the electronic service tool to perform the "DEF Dosing System Accuracy Test".
E. Visually inspect the back flow port of the supply module for a constant flow of DEF.
At least 12 kg (26.5 lb)
per hour.
Result: There is little or no flow from the backflow port of the supply module.
Repair: Replace the DEF Pump module.
Result: The flow rate from the backflow connector is OK.
Repair: If one of the preceding diagnostic codes are logged every time the engine is shut down, either the purging pump is not operating correctly or the DEF pump pressure sensor is faulty. Replace the DEF pump module. Refer to Disassembly and Assembly for the correct procedure.