4387613 | Genuine Cummins® Diesel Exhaust Fluid Tank With Sensor

1. Reduce air pollution

Diesel engines produce nitrogen oxides (NOx), which are harmful pollutants.
DEF is used in the Selective Catalytic Reduction (SCR) system to convert those pollutants into harmless nitrogen and water vapor before they leave the exhaust.

2. Monitor the DEF system

The sensor in the tank helps the vehicle’s computer monitor the DEF system by checking:

Fluid level – how much DEF is left

Temperature – DEF can freeze in cold weather

Fluid quality/concentration (on some vehicles)

This ensures the system is working properly.

3. Warn the driver and protect the engine

The sensor sends information to the engine control system so the vehicle can:

Show a low DEF warning

Detect contaminated or bad DEF

Prevent emissions violations

Avoid damage to the SCR system

If DEF runs out or the system fails, many vehicles will limit engine power or speed until the issue is fixed.

4. Meet emissions regulations

Modern diesel vehicles must follow strict emissions laws set by organizations like the United States Environmental Protection Agency.
The DEF tank and sensor help vehicles stay compliant with these regulations.

1. DEF warning light stays on

• You may see a “Low DEF” or “Service DEF System” message even when the tank is full.

2. Incorrect DEF level reading

• The dashboard may show the tank as empty, full, or stuck at one level regardless of how much DEF is actually inside.

3. Check engine light

• The check engine light may come on due to emissions system errors.

4. Speed or power limited (derate)

• Many diesel vehicles reduce engine power or limit speed if the system thinks DEF is empty or malfunctioning.

5. “No start” countdown message

• Some trucks start a countdown of miles until the vehicle won’t restart if the DEF system problem isn’t fixed.

6. DEF system fault codes

• A scan tool may show emissions-related codes related to DEF level, temperature, or quality.

7. DEF gauge not changing after refill

• You fill the tank but the gauge doesn’t update because the sensor isn’t reporting correctly.