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

• CAT C13 engines
• CAT C15 engines
• 773G / 775G off-highway trucks
• 926M wheel loaders
• 349D / 374D excavators (SCR variants)
• 735 / 740 / 745 articulated trucks (system dependent)
• Various CAT off-highway, mining, and industrial SCR platforms

OEM / Cross reference numbers:

• 441-5128 / 441-5128-03 / 441-5128-04
• 4415128 / 4415127 (related NOx sensor family)
• 5WK96725A (aftermarket reference in some listings)

📌 Verified OEM listing shows this is a Cat NOx Emissions Sensor Group used for SCR closed-loop control.

FUNCTION:

• Measures nitrogen oxide (NOx) levels in exhaust gas
• Sends real-time data to ECU via J1939 communication
• Controls SCR/DEF dosing strategy
• Provides O2 monitoring (<20.9% range) for aftertreatment control
• Enables fault detection (open/short circuit diagnostics)
• Ensures EPA / EU emissions compliance

INSTALLATION POSITION:

• SCR system inlet or outlet NOx sensor (depending on configuration)
• Mounted on exhaust line before or after SCR catalyst
• Common in engine-out and tailpipe-out SCR setups

IMPORTANT NOTE:
Caterpillar 441-5128-04 is part of a smart SCR sensor assembly system, meaning:

• Includes probe + electronics + harness module
• Inlet and outlet sensors are NOT interchangeable
• Different engine applications may require different harness lengths
• ECU calibration defines correct function

Incorrect installation may cause SCR fault codes, derate, or emissions failure.

FAQ:

Q1: Is this inlet or outlet sensor?
A1: It can be used as inlet or outlet depending on CAT C13/C15 SCR configuration.

Q2: What machines does it fit?
A2: CAT 773G, 775G trucks, 926M loader, C13/C15 engines, excavators, mining equipment.

Q3: What are failure symptoms?
A3: SCR warning light, NOx sensor fault codes, engine derate, DEF system errors.

Q4: Are 441-5128-04 and 441-5128 the same?
A4: Yes, 441-5128-04 is a revised version within the same Cat NOx sensor group.

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