5012178R91 | OEM International QLS Sensor, Tank, Def, 7 Gal, Head

Part number is fitted to International / Navistar heavy-duty and medium-duty truck platforms equipped with 7-gallon DEF tanks:

• Class 8 Highway Trucks: International ProStar, LT Series, LoneStar.

• Vocational & Regional Trucks: International WorkStar, DuraStar, HV Series, HX Series.

• Compatible Engine Platforms: Cummins ISX15 / X15, Navistar N13 / MaxxForce engines paired with SCR aftertreatment systems.

1. What is it?

Part is a complete multi-function "header unit" (or pickup module) submerged inside the DEF tank of commercial trucks. It connects the DEF tank directly to the vehicle’s ECM and Selective Catalytic Reduction (SCR) aftertreatment system.

2. Integrated Functions

• Quality & Level Sensing (QLS): Uses an ultrasonic/optical sensor stem to measure real-time DEF fluid level, DEF concentration percentage (ensuring no dilution/contamination), and fluid temperature.

• Fluid Suction & Return Lines: Features stainless steel pickup tubes that transport DEF to the dosing pump and cycle unneeded fluid back to the tank.

• Coolant Heating Loop: Contains built-in coolant coils connected to the engine’s cooling system to thaw frozen DEF (which freezes at 12°F / -11°C).

• In-Tank Filtration: Features a mesh filter screen at the bottom of the pickup tube to block debris before fluid enters the dosing pump.

1. Active Check Engine Light (CEL) & SCR Fault Codes

The engine control module (ECM) detects inaccurate sensor signals or lost J1939 CAN-bus communication from the Quality, Level, and Temperature Sensor (QLS):

• Common Diagnostic Trouble Codes (DTCs):

  • SPN 1761 / FMI 9, 11, 19 (DEF Tank Level - Abnormal Rate of Change / Communication Error)

  • SPN 3364 / FMI 2, 9, 11 (DEF Quality - Incorrect Concentration Detected)

  • SPN 3031 / FMI 9, 11 (DEF Tank Temperature - Data Erratic or Missing)

  • SPN 4364 / FMI 18 (SCR NOx Conversion Efficiency Below Limit)

2. Incorrect DEF Level Gauge Readings

• Symptom: The DEF level gauge on the dash stays stuck at "Full", drops to "Empty" with a full tank, or fluctuates wildly while driving.

• Cause: Internal float failure, ultrasonic sensor stem degradation, or wiring harness corrosion inside the 4-pin connector.

3. False "Poor DEF Quality" Warnings & De-rate Indication

• Symptom: Dash warning alerts indicating "Incorrect DEF Detected" or "Improper Fluid Quality", even after draining and refilling with fresh 32.5% ISO 22241 DEF.

• Consequence: Triggers the vehicle’s de-rate timer, limiting speed (e.g., 55 mph, 5 mph) or reducing engine horsepower until replaced.

4. DEF Tank Freezing in Cold Weather

• Symptom: Fluid inside the tank remains frozen during sub-zero operations, causing DEF pump starvations and pressure faults (SPN 3556).

• Cause: Internal coolant valve failure or clogged heating loop inside the header assembly.