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

• CAT C4.4 engines
• CAT C6.6 engines
• 926M wheel loader
• 938M wheel loader
• 320F / 323F excavators (SCR variants)
• 315 / 316 / 318 series machines
• Various CAT construction and industrial SCR applications

OEM / Cross reference numbers:

• 539-0118
• 539-0117 / 539-0117-03 (related versions)
• CAT NOx Sensor Group family
• 5WK96725A (Continental equivalent platform reference in aftermarket listings)

📌 This is a verified Caterpillar SCR NOx sensor group used for emissions monitoring and DEF control. (parts.cat.com)

FUNCTION:

• Measures nitrogen oxide (NOx) levels in engine exhaust gas
• Sends real-time data to ECU via J1939 communication protocol
• Controls AdBlue/DEF dosing for SCR system efficiency
• Monitors exhaust aftertreatment performance
• Detects system faults (open/short circuit diagnostics)
• Ensures EPA / EU emissions compliance

INSTALLATION POSITION:

• Engine-out (upstream) NOx sensor
• Installed before SCR catalyst in exhaust system
• Works with downstream NOx sensor for full SCR monitoring

IMPORTANT NOTE:
CAT 539-0118 is part of a modular SCR sensor system, meaning:

• Includes probe + electronics + harness assembly
• Not a simple plug-and-play sensor only
• Inlet and outlet sensors are NOT interchangeable
• Calibration differs depending on engine family (C4.4 vs C6.6)
• ECU software defines correct usage

Incorrect installation may trigger SCR faults, engine derate, or emissions errors.

FAQ:

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

Q2: What machines does it fit?
A2: CAT 926M, 938M loaders, C4.4 and C6.6 engines, and SCR-equipped CAT equipment.

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

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

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