4388105 | Genuine Cummins® DEF Doser Pump For EPA17 6.7L ISB/QSB

• 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

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.