Description:
A Diesel Exhaust Fluid (DEF) sensor 4163695C91 is a key component in a diesel vehicle’s emissions control system, specifically within the Selective Catalytic Reduction (SCR) system. The DEF header (also called a DEF tank head or DEF sender assembly) is the unit mounted on or inside the DEF tank. It monitors and manages the Diesel Exhaust Fluid that’s injected into the exhaust to reduce harmful nitrogen oxide (NOx) emissions.

Part Number: 4163695C91
Condition: New
Manufacture/Brand: International

Fits 4163695C91 For Navistar / International
Engines: Cummins QSX15

Specifications 4163695C91:

Electrical Connector: Deutsch DT4 (STD)
Sensor Type: Digital (canbus)
DEF Header Height (IN): 27
DEF Suction Fitting Dia. (IN): 3/8 SAE J2044
DEF Return Fitting Dia. (IN): 5/16 SAE J2044
Coolant Inlet Fitting Dia. (IN): 5/8 Hose Bead
Coolant Outlet Fitting Dia. (IN): 5/8 Hose Bead
In-Tank Filter: 40µ
Tank Interface: 6 Bolt

Purpose of using 4163695C91:

  1.  Monitor DEF Condition

    • Measures DEF level, temperature, and quality (urea concentration).

    • Sends this data to the engine control unit (ECU) so it can adjust DEF injection accurately.

    • Ensures only properly mixed DEF (32.5% urea, 67.5% deionized water) is used — critical for emission compliance.

  2.  Supply DEF to the SCR system

    • The header connects to a DEF pump that draws fluid from the tank and sends it through heated lines to the DEF injector in the exhaust.

    • Without the header’s pickup and delivery system, DEF couldn’t flow properly.

  3.  Maintain DEF Temperature

    • Includes a heater element to prevent DEF from freezing in cold weather.

    • Ensures DEF remains in a liquid state for reliable flow and injection.

  4.  Communicate with the Vehicle’s ECU

    • The header provides sensor data that helps the ECU determine:

      • When to inject DEF

      • How much DEF to inject

      • Whether there are faults (e.g., low DEF, poor quality, or freezing issues)


Signs of a Bad Diesel Exhaust Fluid Sensor 4163695C91:

1. Warning Lights and Fault Codes

  • “Check Engine” light or “DEF system fault” message on the dash.

  • SCR or emissions-related fault codes (often starting with P20xx, such as P203F, P205B, P206A, P207F).

  • DEF quality sensor errors or temperature sensor circuit faults stored in the ECM.

  • “Service DEF system” or “Vehicle will derate in XXX miles” messages.

2. Incorrect DEF Level Reading

  • DEF gauge shows empty or full all the time, regardless of actual level.

  • Gauge fluctuates or drops suddenly after refilling the DEF tank.
    Cause: DEF level sensor inside the header is malfunctioning or covered in crystallized DEF.

3. DEF Freezing or Not Thawing

  • In cold weather, the system takes too long to thaw or never thaws at all.

  • The engine may derate because frozen DEF can’t be injected.
    Cause: The heater element in the DEF header has failed.

4. DEF Quality or Concentration Errors

  • ECU reports poor DEF quality or incorrect urea concentration even when fresh DEF is used.
    Cause: The quality sensor inside the header is faulty or contaminated with crystallized DEF.

5. Engine Derate or Power Limitation

  • The truck goes into limp mode or reduces speed (e.g., limited to 5 mph) after warnings are ignored.
    Cause: The ECM forces derate to prevent emissions violations if it detects the SCR system isn’t working properly.

6. Crystallization or Contamination

  • Visible white crystals or buildup around the DEF tank or header connector.

  • Poor electrical contact due to corrosion or DEF leakage.
    Cause: DEF exposure to air causes crystallization, which can damage sensors or block passages.