A0001404378 | Genuine Detroit Diesel® DEF Pump HDEP Air Assisted

A DEF pump (Diesel Exhaust Fluid pump) is an electrically controlled pump that draws DEF from the tank, pressurizes it, and delivers it in a precisely controlled amount to the SCR emissions system on a diesel engine. Related Part Numbers: RA0001404378, 0001404378

General Specifications

Purpose & Function

1. Deliver DEF to the Exhaust

The pump:

• Draws DEF from the tank

• Pressurizes it

• Sends it to the DEF injector

Without the pump, DEF cannot reach the exhaust stream.

2. Control Emissions (Reduce NOx)

Diesel engines produce nitrogen oxides (NOx), which are harmful pollutants.

When DEF is injected into the exhaust:

• It turns into ammonia

• Ammonia reacts with NOx

• Converts it into nitrogen and water vapor (safe gases)

Engine manufacturers like Cummins Inc. and Detroit Diesel rely on DEF pump systems to meet EPA emissions regulations.

3. Maintain Proper System Pressure

The DEF pump:

• Keeps correct pressure in the DEF lines

• Adjusts flow based on engine load

• Communicates with the engine control module (ECM)

• More engine load = more DEF required
• Less engine load = less DEF required

4. Prevent Crystallization & Freezing

DEF:

• Freezes at 12°F (-11°C)

• Can crystallize when exposed to air

The pump system often:

• Includes heaters

• Purges lines after shutdown

• Prevents DEF buildup in injectors

Signs of a Bad DEF Pump

1. Check Engine Light

• Check engine light comes on

• DEF or emissions warning appears

• “Service DEF System” message

The ECM monitors DEF pressure and flow. If pressure is too low or too high, it sets a fault code.

Systems used by manufacturers like Cummins Inc. and Detroit Diesel are very sensitive to DEF pressure faults.

2. Engine Derate (Reduced Power)

• Truck loses power

• RPM limited

• Speed limited (often 55 mph or less)

If the problem isn’t fixed, the vehicle may enter severe derate mode.

3. DEF Pressure Codes

Common scan tool codes:

• Low DEF pressure

• Unable to build pressure

• DEF pump performance fault

• SCR efficiency fault

A scan tool will show pressure not reaching spec.

4. Hard Starting After Shutdown

Some DEF systems purge fluid after shutdown.
If the pump fails:

• Lines may stay pressurized

• DEF may crystallize in injector

• System may struggle during next startup

5. DEF Leaks or Crystallization

• White crystal buildup around pump or fittings

• Wet DEF lines

• Strong ammonia smell

Crystallized DEF is a common failure cause.

6. Excessive DEF Consumption

• Using more DEF than normal

• SCR overcompensating due to pressure problems

7. Frozen DEF System (Cold Weather Issues)

Since DEF freezes at 12°F (-11°C):

• Pump heater failure may cause pressure faults

• DEF system won’t prime

About Detroit Diesel

Detroit Diesel is a leading American manufacturer of heavy-duty diesel engines, transmissions, and aftertreatment systems, primarily for the commercial trucking industry. Founded in 1938 and now a subsidiary of Daimler Truck North America, Detroit is best known for its DD Series engines — including the DD13, DD15, and DD16 — which power Freightliner and Western Star trucks.

Detroit also produces advanced technologies such as Detroit™ Axles, Detroit™ Connect telematics, and integrated powertrains, offering fleet operators improved fuel efficiency, uptime, and diagnostics. The company is headquartered in Detroit, Michigan, and continues to play a central role in modernizing emissions systems and performance standards in heavy-duty transportation.