5373865 | Genuine Cummins® Fluid Supply Doser Module

Medium-Duty (6.7L Engines):

• Platforms: Cummins ISB6.7, QSB6.7.

• Common Part Numbers	4387304, 5273338, 4375026.

• Vehicles	School buses (Blue Bird, Thomas), Freightliner M2 106, Ford F-650/750, and medium-duty Ram trucks (Chassis Cab).

Heavy-Duty (12L & 15L Engines)

• Platforms: Cummins ISX15, X15, QSX15, ISX12.

• Common Part Numbers	5511749, 4394627, 4387658.

• Vehicles	Class 8 trucks like Kenworth T680, Peterbilt 579, Freightliner Cascadia, and International LT Series.

Industrial/Tier 4 Platforms

• Platforms: Cummins B4.5, F3.8, L9.

• Common Part Numbers	5418806, 5375352 (This part number is very close to the one you mentioned earlier).

Pressurization: The module draws DEF from the storage tank and pressurizes it (usually to around 9 bar / 130 psi) so it can be finely misted by the injector.

Purge Cycle: One of its most important features is the "purge" function. When the engine is turned off, the module pumps the remaining fluid back into the tank. This prevents the DEF from freezing or crystallizing inside the lines, which could crack the module.

Filtering: It contains an internal main filter to protect the precise dosing mechanism from contaminants or crystallized urea.

Electronic Control: It communicates directly with the Engine Control Module (ECM) via the CAN bus to determine exactly how much fluid is needed based on engine load and NOx sensor readings.

DEF Pressure Faults: If the module cannot reach or maintain its operating pressure (typically around 130 psi / 9 bar), the ECM will trigger fault codes like 3558 or 3559. You may hear the pump "hunting" or running constantly without building pressure.

Crystallization Leaks: White, chalky deposits around the module's fittings or the vent hole indicate that DEF is leaking. Once the fluid dries and crystallizes, it can seize the internal pump mechanism or damage the electrical circuit board.

Failed Purge Cycle: If you don't hear the characteristic "clicking" or humming sound of the pump running for 30–60 seconds after you turn off the ignition, the purge cycle has failed. This usually leads to frozen or clogged lines in cold weather.

Low DEF Consumption: If you notice that you are rarely needing to refill your DEF tank, the module is likely not delivering fluid. This will eventually lead to a NOx conversion error and a 5-mph derate.

Electrical Communication Codes: Fault codes like 3591 indicate the module has lost communication with the engine via the CAN bus, often due to internal short-circuiting from moisture or vibration.