NOx Sensor 21244501

BG 990594 (OE 21244501): function on the vehicle

NOx Sensor 21244501 is supplied by BEST GROWTH under part number 990594, cross-referenced to OE 21244501, 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 990594 is built to the position defined by its OE application on a 24V electrical system in truck service on the platform from Volvo. Position, calibration and connector layout are part of the specification, so a part that physically fits is not automatically the correct part.

The measuring cell is consumable. Soot loading, silicone contamination and repeated thermal shock all shorten its life, which is why a sensor can drift for months before it sets a hard code.

Fitment for Volvo and OE cross reference

BG 990594 replaces 2 OE references: 21244501 and 5WK9 6664A, covering cross applications. Always confirm the number printed on the removed part, including any supersession issued by the vehicle manufacturer.

Recorded vehicle coverage for 990594 includes Volvo, typically on FH / FM / FL / FE Truck. 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 21244501 and quoting the number on your part lets our technical team confirm the variant before despatch.

Symptoms that lead to replacing 21244501

These complaints bring a vehicle in with the Volvo nox sensors under suspicion. None of them prove BG 990594 has failed on its own, which is why the checks below matter before a replacement is ordered.

• 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
• DEF over-consumption with no visible leak

Checks before fitting BG 990594

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

• Read the sensor's own dew-point release time — a cell that never heats is a supply or module fault.
• Verify DEF concentration with a refractometer before blaming the measuring cell.
• Check for a pending software or parameter update for the sensor control module on that platform.
• 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.

Quality, packaging and ordering 990594

BG 990594 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 21244501 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 990594 replace OE 21244501?

Yes. BG 990594 is listed against 21244501 and 5WK9 6664A. Confirm the number printed on the removed part and any manufacturer supersession before ordering.

Which vehicles does BG 990594 fit?

Recorded coverage includes Volvo. 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 990594.