FITMENT:
Compatible with Caterpillar machines equipped with SCR aftertreatment systems, including:

• CAT C6.6 engines
• 320F / 323F excavators
• 315F / 316F / 318F series machines
• 924K / 926M / 938M loaders (SCR variants)
• 740 / 745 articulated trucks (system dependent)
• Various CAT construction and industrial SCR platforms

OEM / Cross reference numbers:

• 539-0117 / 539-0118 / 539-0117-03
• 5WK96725A (Continental equivalent platform reference)
• CAT NOx Sensor Group (Engine-out SCR system)

📌 Verified OEM source confirms this is a Cat NOx Emissions Sensor Group (engine-out) used for SCR closed-loop control.

FUNCTION:

• Measures nitrogen oxide (NOx) levels in engine exhaust (before SCR catalyst)
• Sends real-time data to ECU via SAE J1939 communication
• Provides feedback for DEF/AdBlue dosing control
• Measures oxygen content in exhaust gases (<20.9%)
• Supports self-diagnostics for wiring faults (open/short circuit detection)
• Ensures EPA / EU emissions compliance

INSTALLATION POSITION:

• Engine-out (upstream) NOx sensor
• Mounted before SCR catalyst in exhaust system
• Works together with downstream NOx sensor for full emissions control

IMPORTANT NOTE:
Caterpillar NOx sensors like 539-0117 are part of a smart sensor assembly system, meaning:

• Includes probe + electronics + harness module
• Not a simple plug-only sensor
• Must match engine family (C6.6 / C7 / C9 calibration differences)
• Inlet/outlet sensors are NOT interchangeable
• ECU software defines correct configuration

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

FAQ:

Q1: Is this inlet or outlet sensor?
A1: 539-0117 / 539-0118 is typically an engine-out (inlet) NOx sensor.

Q2: What machines does it fit?
A2: CAT 320F, 323F, and other C6.6 powered construction machines.

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

Q4: Are 539-0117 and 539-0118 interchangeable?
A4: They are part of the same sensor family but may differ in calibration or position.

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