2515986C1 | Genuine International® Def SENSOR, 16/23G, QLS SSI

-DEF Header Height (IN)
25

-DEF Return Fitting Dia. (IN)
5/16 SAE J2044

-Coolant Outlet Fitting Dia. (IN)
5/8 Hose Bead

-Tank Interface
6 Bolt

-Electrical Connector
Deutsch DT4 (STD)

-Sensor Type
Digital (canbus)

-DEF Suction Fitting Dia. (IN)
3/8 SAE J2044

-Coolant Inlet Fitting Dia. (IN)
5/8 Hose Bead

-In-Tank Filter
40µ

Compatible Vehicle Models & Applications

• Vehicle Compatibility: Designed for Navistar International® medium and heavy-duty trucks equipped with 16-gallon (16G) or 23-gallon (23G) DEF tank configurations.

  • International Models: LT Series, RH Series, MV Series, HV Series, ProStar, Durastar, WorkStar, and LoneStar models.

  • Bus Applications: IC Bus® CE/RE Series school and commercial buses.

• Engine Architecture: Fits trucks powered by Navistar International A26 engines, as well as Cummins® ISB6.7, L9, ISX15, and X15 diesel engines using standard Navistar/IC Bus DEF tank headers.

1. What is it?

The is a combination sensing and pickup unit installed inside 16-gallon (16G) and 23-gallon (23G) Diesel Exhaust Fluid (DEF) tanks. It continuously gathers fluid data and communicates with the vehicle’s Engine Control Module (ECM) via the J1939 CAN bus network to maintain proper Selective Catalytic Reduction (SCR) emission control.

2. Core Functions

• DEF Level Sensing: Uses an ultrasonic sensor to monitor remaining DEF volume and report accurate levels to the driver dashboard.

• DEF Quality & Concentration Sensing: Monitors urea concentration (ensuring the standard ~32.5% purity) to protect the SCR system from diluted or improper fluids.

• Temperature Monitoring & Thawing: Measures DEF temperature and utilizes an internal coolant loop connection to defrost frozen DEF during cold weather operations.

• Fluid Delivery & Return: Features integrated pickup and return ports to feed fluid to the DEF dosing unit and handle overflow return.

1. Engine Power Derate & Speed Restrictions

When sensor failure prevents the ECM from verifying proper SCR operation, the vehicle enters a forced inducement protocol:

• Initial Warning: Check Engine light and Stop Engine / Emissions lights turn on with audible chimes.

• Power Derate: Engine horsepower and torque are reduced by 25% to 40%, making it difficult to haul heavy loads or maintain highway speeds.

• Final Speed Limit (5 MPH Mode): If unaddressed, the vehicle will eventually be restricted to a 5 mph (8 km/h) low-idle crawl mode.

2. Diagnostic Trouble Codes (DTCs)

Connecting a diagnostic tool (such as Navistar ServiceMaxx or Cummins Insite) will reveal specific J1939 fault codes:

• SPN 1761 / FMI 9 or 19: DEF Tank Level - Abnormal Update Rate or Error.

• SPN 3031 / FMI 2 or 9: DEF Tank Temperature - Data Erratic or Incorrect.

• SPN 3516 / FMI 2 or 12: DEF Concentration / Quality - Bad Device or Component.

• SPN 3364 / FMI 9: Improper DEF Quality Detected.

3. Inaccurate or "Stuck" DEF Level Gauge

A failed ultrasonic sensing element inside the SSI unit causes erratic gauge behavior:

• The gauge on the dashboard may remain frozen at 100% (Full) or drop immediately to 0% (Empty) despite a full tank.

• Frequent "DEF Refill Needed" warnings pop up unexpectedly.

4. False "Poor DEF Quality" Alerts

An internal failure of the concentration sensor sends corrupted density signals to the ECM. Even if the tank is filled with fresh, ultra-pure DEF (~32.5% urea), the cluster display will warn of "Incompatible or Contaminated DEF Fluid."

5. DEF Freeze & Thaw Failure in Cold Climates

If the internal temperature thermistor or coolant heating valve circuit fails:

• In freezing temperatures, the ECM cannot accurately detect if DEF is frozen and will fail to trigger coolant flow to thaw it.

• The dosing pump runs dry or becomes starved of liquid DEF, leading to active dosing system errors.