4377364RX | Genuine Cummins® DEF Doser Pump

A DEF Doser Pump (Diesel Exhaust Fluid doser pump) 4377364RX is a component in modern diesel vehicles that injects Diesel Exhaust Fluid (DEF) into the exhaust system to reduce harmful emissions.

General Specifications

Purpose & Function

• Delivers the correct amount of Diesel Exhaust Fluid (DEF)
  It pulls DEF from the tank and sends a precise, pressurized amount into the exhaust system.

• Reduces harmful NOx emissions
  Inside a Selective Catalytic Reduction (SCR) system, the DEF turns into ammonia and reacts with nitrogen oxides (NOx), converting them into:

  • Nitrogen (harmless)

  • Water vapor (harmless)

• Ensures the system works efficiently
  It carefully controls dosing so:

  • Too little DEF doesn’t cause emissions failures

  • Too much DEF doesn’t waste fluid or damage components

Signs of a Bad DEF Doser Pump

1. Check Engine Light (CEL)

The most common sign.
You’ll usually see fault codes related to:

• SCR system performance

• DEF pressure too low

• DEF dosing malfunction

• NOx efficiency below threshold

2. Emissions Warning Message

You may see messages like:

• “Exhaust Fluid System Fault”

• “Service DEF System”

• “Poor DEF Quality” (even when fluid is good)

3. Reduced Engine Power (Limp Mode)

If the system detects improper DEF dosing, the vehicle may:

• Limit engine power

• Limit top speed

• Start a countdown to limited starts or no restart

4. DEF Pressure Problems

A failing pump may not build proper pressure, causing:

• Rough engine performance in some cases

• SCR efficiency faults

• Inconsistent DEF consumption

5. Excessive or No DEF Usage

• Using too much DEF (over-dosing)

• Using almost none (under-dosing)

Either condition can indicate a pump issue.

6. Crystallized DEF Around Components

If the pump or lines leak, you might see:

• White crystal buildup near DEF lines or pump

• DEF smell near the vehicle

7. Vehicle Won’t Restart

In many modern diesel systems, if the SCR fault is not fixed:

• The vehicle may eventually refuse to start after shutdown.

About Cummins

Cummins is a leading American manufacturer of diesel and natural gas engines, as well as power generation systems and emissions solutions. Founded in 1919 and headquartered in Columbus, Indiana, Cummins is known globally for its durable, high-performance engines used in trucks, buses, construction equipment, agriculture, and power systems.

The brand is widely respected for its innovation in clean diesel technology, including aftertreatment systems, turbochargers, and advanced electronics that help reduce emissions while maximizing engine efficiency and reliability.