NOx Sensor A000 905 31 09

BG 201291 (OE A000 905 31 09): function on the vehicle

NOx Sensor A000 905 31 09 is supplied by BEST GROWTH under part number 201291, cross-referenced to OE A000 905 31 09, as a direct-fit aftermarket nox sensors. In service it runs a heated zirconia measuring cell inside its own sensor control module, converts the raw cell current into a NOx value in ppm, and publishes it on the bus. The engine controller cannot calculate dosing quantity or conversion efficiency without a plausible signal from it.

BG 201291 is built to the position defined by its OE application on a 12V electrical system in passenger car service on the platform from Mercedes-Benz. Position, calibration and connector layout are part of the specification, so a part that physically fits is not automatically the correct part.

Fitting position matters as much as the part number: upstream and downstream references often share a housing but carry different calibration data and cable lengths.

Fitment for Mercedes-Benz and OE cross reference

BG 201291 replaces 2 OE references: A000 905 31 09 and SNS424B, covering cross applications. Always confirm the number printed on the removed part, including any supersession issued by the vehicle manufacturer.

Recorded vehicle coverage for 201291 includes Mercedes-Benz, typically on A-Class A180d / A200d / A220d 2018-. Coverage lists are a starting point for identification, not a substitute for checking the OE number on the vehicle.

Where several OE numbers appear against one BG reference, they are supersessions or regional variants of the same specification. Ordering by A000 905 31 09 and quoting the number on your part lets our technical team confirm the variant before despatch.

Symptoms that lead to replacing A000 905 31 09

These complaints bring a vehicle in with the Mercedes-Benz nox sensors under suspicion. None of them prove BG 201291 has failed on its own, which is why the checks below matter before a replacement is ordered.

• sensor value frozen at a fixed number once the exhaust warms up
• dosing shut-down after a few minutes of steady-state running
• upstream and downstream values reading almost identically under load
• intermittent fault that clears after the engine cools and returns when hot
• SCR efficiency below threshold or NOx-signal-implausible fault codes

Checks before fitting BG 201291

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

• After fitting, run the manufacturer's adaptation or relearn so stored efficiency counters reset.
• 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.

Quality, packaging and ordering 201291

BG 201291 is manufactured and tested to aftermarket replacement standards, with electrical, leakage and functional testing carried out before packing on the 12V specification. Bulk and retail packaging, private-label cartons and customer-specific labelling are available for distributors and workshop groups.

Send OE A000 905 31 09 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 201291 replace OE A000 905 31 09?

Yes. BG 201291 is listed against A000 905 31 09 and SNS424B. Confirm the number printed on the removed part and any manufacturer supersession before ordering.

Which vehicles does BG 201291 fit?

Recorded coverage includes Mercedes-Benz. It is supplied as a direct-fit aftermarket nox sensors on 12V 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 201291.