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Check the code position before you buy. An oxygen sensor is the small probe in your exhaust that reports leftover oxygen, and your 1.6-litre Hyundai or Kia carries two of them. The 39210-2B370 is the rear one, so its codes are P0140-P0144.

Wrong-position orders are the most common mistake here. The 39210-2B370 oxygen sensor for the 2015-2019 Hyundai ix35, Tucson, and Kia Sportage 1.6L fits the rear spot only. P0130-P0134 and P0171 usually convict something else, so read on first.

What the 39210-2B370 is, and where it sits

It is a rear sensor, and the catalogs say so. Hyundai lists the 39210-2B370 as Sensor Assembly-Oxygen, RR (RR means rear), application 2016-2018 Tucson.

It is a four-wire heated unit: two heater wires, one signal, one ground. The OE reference is 39210-2B330, and 39210-2B220, 2B330, and 2B370 are interchangeable suffixes of the same series.

Rear placement is the diagnosis, not a footnote. The part sits after the catalytic converter, in the Bank 1 Sensor 2 spot. The converters, pipes, and clamps around it live in the exhaust emission systems collection.

Two sensors, one loop, two different jobs

One closed fuel-control loop, two sensors in it. The upstream one reads the exhaust before the catalyst and steers fuel. The rear one reads what the catalyst lets through and grades the converter.

• Upstream (Bank 1 Sensor 1): reports mixture direction many times a second, and the computer trims injector pulse in answer. Its codes are P0130-P0134.
• Rear (Bank 1 Sensor 2): a flat, lazy trace is what a healthy converter produces. Its codes are P0140-P0144.
• Not interchangeable: on GDI and T-GDI engines the upstream part is a wideband "air fuel ratio sensor", a different part by design.

That split explains every code here: upstream codes convict the fuel-control loop, rear codes convict the sensor or the converter. The guide to how catalytic converters handle emission control explains the oxygen storage behind that flat trace.

P0130 to P0134: what each code convicts

All five point at the upstream sensor. Each code describes a different failure. The table is the short read.

Check the heater first. An element that never reaches its roughly 600 °F (315 °C) operating class cannot switch at all. An open heater or its fuse mimics a dead sensor, and five minutes at the connector settles it.

P0131 and P0132 are bias codes, and bias has causes outside the element:

• An exhaust leak ahead of the sensor pulls in fresh air and fakes a lean reading.
• A leaking injector or a dragging purge valve fakes a rich one.
• Silicone from carelessly applied RTV sealant bakes into a glaze that blocks the reference air path.

The upstream and downstream O2 sensor guide with DTC mapping runs the same code-by-code logic on a Chevrolet platform.

P0171 is a fuel-trim story, not a sensor verdict

P0171 means System Too Lean (Bank 1). Fuel trim is the computer's running correction: short-term is the second-by-second nudge, long-term is the learned average on top. Their sum should stay inside roughly plus or minus 10 percent.

The idle-versus-rpm split is the fastest triage here. Watch short-term plus long-term trim on a scan tool:

• Trims high at idle, improving as revs rise → vacuum leak. Check the intake boots, the brake booster hose, and the purge valve.
• Trims near zero at idle, climbing 15 to 20 percent under load → fuel delivery, or a mass air flow sensor reporting low.
• Normal trims with a sensor code → the sensor itself.

One trap deserves its own line. An exhaust leak upstream of the sensor mimics a vacuum leak, because both feed the sensor oxygen that never went through the engine.

Matching the replacement to your exact 1.6 engine

The 1.6 badge hides three engines, and the sensor follows the engine code, not the badge. Read it off the block or the build sticker:

• G4FD — the naturally aspirated 1.6 GDI at about 140 PS, behind the ix35 (LM) 2010-2015.
• G4FG — its port-injected 1.6 MPI sibling at about 132 PS, same cars.
• G4FJ — the 1.6 T-GDI turbo at roughly 177 hp, behind the Tucson (TL) 2016-2018 and the Sportage (QL) 2016-2019.

The turbo engine runs hotter exhaust and a different sensor spec — not interchangeable with the naturally aspirated 1.6.

On another Gamma platform? Order the part that actually fits it:

• Kia Sportage or Hyundai Sonata 2.4L → the 39210-2G100 upstream oxygen sensor.
• 2017-2020 Elantra, 2019-2021 Veloster, or 2010-2011 Soul → the 3921002950 O2 sensor.
• Hyundai Elantra 2.0L → the 39210-23910 upstream lambda sensor, which crosses to 234-5047.
• 2001-2011 Hyundai Accent, or 2006-2011 Kia Rio and Rio5 → the 39210-22610 oxygen sensor.

Frequently asked questions