A-Premium Downstream O2 Oxygen Sensor for Hyundai & Kia — B1S2 Heated 4‑Wire (Post‑Catalyst)

The A-Premium downstream oxygen sensor (B1S2) is a direct-fit, 4-wire heated O2 sensor designed to replace faulty downstream sensors on many Hyundai and Kia models for accurate exhaust monitoring and emissions performance.

This downstream (post-catalyst) oxygen sensor from A-Premium is built as a threaded, heated 4-wire unit intended to match OE fit and function for a range of Hyundai and Kia vehicles. It comes boxed with one oxygen sensor and multiple reference numbers for cross-checking fit (250-24878 / 350-34630). Before ordering, confirm your exact vehicle year, engine size and emissions spec in the fitment selector.

Which vehicles and engines does this A-Premium downstream sensor fit?

This sensor covers specific Hyundai and Kia models across several model years. Fitment varies by engine displacement, transmission type and emissions configuration — some listings exclude federal emissions variants.

• Hyundai Sonata 2009–2010 2.4L and 2011–2015 2.4L FHEV (select years)
• Hyundai Tucson 2010–2015 (2.0L and 2.4L depending on year and transmission)
• Hyundai Genesis Coupe 2010–2014 2.0L; Santa Fe/Santa Fe Sport 2010–2016 2.4L ranges
• Kia Forte/Forte Koup 2010–2013 (2.0L and 2.4L auto); Optima/Optima Koup and Sorento/Sportage fits for listed years

How does the sensor’s specification affect installation and performance?

The unit is a heated oxygen sensor with a threaded mounting and a male connector, intended to plug into existing wiring harnesses on compatible vehicles. The heater circuit speeds warm-up for quicker feedback to the engine control module; the 4-wire design supports separate heater and signal paths for stable readings.

• Wire count: 4 wires (separate heater and signal lines)
• Sensor type: heated zirconia-style oxygen sensor for post-catalyst use
• Mounting: threaded installation into the downstream bung
• Connector: male-style plug to mate with OEM harness

What reference numbers and part-check tips should I use to make sure it’s correct?

Compare the A-Premium reference numbers and the physical connector to your existing part before purchase. Use the listed reference numbers with your VIN or OE part number to confirm compatibility and avoid ordering the wrong emissions variant.

• Listed references: 250-24878, 350-34630, 25024878, 35034630
• Verify VIN, engine size, year and emissions type in the fitment tool
• Check that your vehicle uses a downstream B1S2 sensor (post-catalytic) before buying

What should I know about installation and maintenance?

Installation requires removing the old sensor from the downstream port and torquing the new threaded sensor to spec; avoid crossing threads and test for fault codes after replacement. If the harness or connector shows corrosion or damage, repair or replace it to ensure reliable signals.

• Install using proper oxygen-sensor socket and torque values; anti-seize may be included or applied per instructions
• Clear codes and perform a drive cycle to confirm system readiness after replacement
• Do not use penetrating sprays on the electrical connector; inspect wiring for heat or abrasion damage

Who this is for: This A-Premium downstream O2 sensor is aimed at DIY mechanics, independent shops and fleet technicians who need a direct-fit, heated B1S2 replacement for compatible Hyundai and Kia cars and SUVs. It's appropriate for anyone replacing a failed downstream oxygen sensor who has confirmed vehicle fitment details and wants a boxed, four-wire threaded unit with standard male connector compatibility.