2523590C91 | Genuine International® Def Quality Sensor

DEF Header Height (IN)
18

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

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

Tank Interface
6 Bolt

Compatible Vehicles & Engines

• Vehicle Compatibility: Engineered for Navistar International® medium and heavy-duty trucks equipped with a 15-gallon DEF tank configuration.

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

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

• Engine Architecture: Compatible with Navistar International A26 engines as well as Cummins® ISB6.7, L9, ISX15, and X15 diesel engines utilizing standard Navistar/IC Bus SCR systems.

1. What is it?

Part is a factory replacement assembly that includes the 15-gallon polyethylene fluid tank alongside an integrated SSI Quality Level Sensor (QLS) header unit. It stores Diesel Exhaust Fluid (AdBlue) and actively relays fluid metrics to the vehicle’s Engine Control Module (ECM) via the J1939 CAN bus network to manage the Selective Catalytic Reduction (SCR) system.

2. Integrated Components & Features

• 15-Gallon Heavy-Duty Reservoir: Chemical-resistant polyethylene tank designed to resist cracking and harsh environments.

• Ultrasonic DEF Level Sensing: Continuously measures remaining DEF volume to display accurate tank levels on the dashboard.

• Urea Concentration / Quality Monitoring: Ensures fluid maintains the required ~32.5% urea concentration to prevent SCR catalytic poisoning.

• Fluid Temperature & Thawing Circuit: Monitors fluid temperature and uses an internal coolant loop connection to melt frozen DEF in cold winter weather.

• Suction & Return Lines: Includes quick-connect ports for fluid suction to the dosing pump and excess return flow back into the tank.

1. Engine Power Derate & Forced Speed Restrictions

Because emission regulations strictly enforce SCR system operation, a failure in the JKA03703 assembly triggers progressive engine derates:

• Initial Warning: Check Engine and Stop Engine / Emissions lights illuminate on the instrument panel with audible warning chimes.

• Power Reduction: Engine horsepower and torque drop by 25% to 40%, significantly impairing highway driving and heavy hauling.

• 5 MPH (8 km/h) Low-Idle Lockout: If the fault is ignored past the countdown timer, the truck is forced into a 5 mph crawl mode.

2. Diagnostic Trouble Codes (DTCs)

Connecting Navistar ServiceMaxx or Cummins Insite diagnostic software will pull specific J1939 fault codes associated with the SSI QLS tank header:

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

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

3. Incorrect or Stuck DEF Level Gauge

A failed ultrasonic level circuit inside the SSI QLS sensor header causes improper readings on the dash:

• The DEF level gauge stays stuck at 100% (Full) or drops instantly to 0% (Empty) despite the 15-gallon tank being completely full.

• Repeated "Refill DEF Tank" alerts trigger unexpectedly.

4. False "Poor DEF Quality" Alerts

An internal failure in the concentration sensor sends bad urea density readings to the ECM:

• The dashboard displays warnings like "Incompatible DEF Detected" or "Service DEF System" even when filled with clean, high-purity fluid (~32.5% urea).

5. DEF Tank Cracks, Leaks, or Freezing Issues

Because includes both the 15-gallon tank shell and the header unit:

• Physical Damage: Cracks or impact damage on the polyethylene tank result in visible DEF fluid leaks (evidenced by white crystalline urea deposits around the tank base).

• Heating Loop Failure: In freezing weather, if the internal thermistor or coolant heating loop fails, frozen DEF cannot thaw, causing dosing pump starvation and active SCR pressure codes.