FITMENT:
Compatible with Caterpillar engines and machines equipped with SCR (Selective Catalytic Reduction) systems, including:

• CAT C13 / C15 engines
• 349D / 374D / 390F excavators
• 785 / 789 / off-highway trucks
• D6 / D7 / D8 / D9 track-type tractors
• Motor graders, loaders, and industrial SCR-equipped machines
• Marine and generator CAT C13/C15 platforms

OEM / Cross reference numbers:

• 441-5127 / 441-5127-03
• 4415127 / 441-5128 / 441-5129 (related sensor family variants)
• 5WK96725A (aftermarket equivalent in some listings)
• CAT part family: NOx Sensor Group (engine-out SCR sensor)

SOURCE CONFIRMATION:
Caterpillar NOx sensor 441-5127 is an engine-out SCR NOx sensor assembly, used to measure exhaust nitrogen oxide levels and provide feedback to the aftertreatment control system over J1939 communication.

It is a complete NOx sensor group (probe + electronics + harness) designed specifically for closed-loop SCR emissions control.

FUNCTION:

• Measures nitrogen oxide (NOx) levels in engine exhaust
• Sends real-time data to ECU via J1939 CAN network
• Provides feedback for SCR dosing control (DEF/AdBlue system)
• Self-diagnosis of open/short circuits in sensor circuit
• Supports emissions compliance for off-highway EPA / EU Stage systems

INSTALLATION POSITION:

• Engine-out (upstream) NOx sensor in SCR system
• Mounted before SCR catalyst (pre-catalyst position)
• Works in combination with downstream NOx sensor

IMPORTANT NOTE:
CAT NOx sensor 441-5127 is part of a modular sensor group system, meaning:

• Sensor includes electronics + probe + wiring harness
• Must match correct engine configuration (C13 vs C15 calibration)
• Inlet and outlet sensors are NOT interchangeable
• ECU software defines correct sensor behavior

Incorrect installation can cause SCR faults, derate, or emissions errors.

FAQ:

Q1: Is this inlet or outlet sensor?
A1: 441-5127-03 is typically used as an engine-out (inlet) NOx sensor.

Q2: What machines does it fit?
A2: CAT C13, C15 engines, excavators (349D, 374D), off-highway trucks, and industrial equipment.

Q3: What are failure symptoms?
A3: SCR warning light, NOx sensor fault codes, engine derate, poor AdBlue dosing.

Q4: Are 441-5127 and 441-5127-03 the same?
A4: Yes, 441-5127-03 is a revision/version of the same CAT NOx sensor group.

Q5: Does installation require programming?
A5: Some CAT machines require SCR calibration reset after replacement.