NOx Sensor 441-5127-03

BG 201171 (OE 441-5127-03): function on the vehicle

NOx Sensor 441-5127-03 is supplied by BEST GROWTH under part number 201171, cross-referenced to OE 441-5127-03, as a direct-fit aftermarket nox sensors. In service it measures nitrogen-oxide concentration and residual oxygen in the exhaust stream and reports both values to the aftertreatment controller over the vehicle data bus. Upstream and downstream readings together set DEF dosing quantity and score SCR conversion efficiency.

BG 201171 is built to the position defined by its OE application on a 24V electrical system on the platform from Caterpillar. Position, calibration and connector layout are part of the specification, so a part that physically fits is not automatically the correct part.

Cable length and connector keying are part of the specification. A cell with correct electrical output but the wrong lead length will not route to the OE bracket.

Fitment for Caterpillar and OE cross reference

BG 201171 replaces 1 OE reference: 441-5127-03. Always confirm the number printed on the removed part, including any supersession issued by the vehicle manufacturer.

Recorded vehicle coverage for 201171 includes Caterpillar, typically on Engine C4.4 / C7.1. Coverage lists are a starting point for identification, not a substitute for checking the OE number on the vehicle.

Quote the number printed on your part with the engine code when you enquire; a single-reference part is the most common source of ordering errors when a platform received a mid-life update.

Symptoms that lead to replacing 441-5127-03

These complaints bring a vehicle in with the Caterpillar nox sensors under suspicion. None of them prove BG 201171 has failed on its own, which is why the checks below matter before a replacement is ordered.

• intermittent fault that clears after the engine cools and returns when hot
• SCR efficiency below threshold or NOx-signal-implausible fault codes
• DEF over-consumption with no visible leak
• torque derate or speed inducement with a full, in-spec DEF tank
• no communication with the sensor control module after a cold start

Checks before fitting BG 201171

Aftertreatment faults are usually system faults. Working through these checks prevents a repeat failure after the new nox sensors is fitted.

• Compare upstream and downstream NOx readings warmed and under load — idle values prove nothing.
• Confirm supply voltage, ground quality and bus termination before condemning the sensor module.
• Inspect the harness for heat damage and the connector for moisture and green corrosion.
• Check for exhaust leaks ahead of the sensor boss; a diluted sample reads low NOx.
• Read the sensor's own dew-point release time — a cell that never heats is a supply or module fault.

Quality, packaging and ordering 201171

BG 201171 is manufactured and tested to aftermarket replacement standards, with electrical, leakage and functional testing carried out before packing on the 24V specification. Bulk and retail packaging, private-label cartons and customer-specific labelling are available for distributors and workshop groups.

Send OE 441-5127-03 or the number printed on your part, the engine code and the vehicle identification number with your enquiry, and our technical team will confirm the correct reference, current stock position and lead time before you commit to an order.

Frequently asked questions

Does BG 201171 replace OE 441-5127-03?

Yes. BG 201171 is listed against 441-5127-03. Confirm the number printed on the removed part and any manufacturer supersession before ordering.

Which vehicles does BG 201171 fit?

Recorded coverage includes Caterpillar. It is supplied as a direct-fit aftermarket nox sensors on 24V systems. Adaptation, reset or relearn procedures required by the vehicle manufacturer still apply after installation.

Does this fault code always mean the nox sensors has failed?

No. Exhaust leaks, wiring and connector damage, reductant quality, dosing performance and upstream engine faults can all produce the same codes. Validate those inputs before replacing BG 201171.